72 ROBERTSON-“RESEARCH IN THE 1NFRA:RED” DEBATE-“DRY -CLEANING” [fifaf‘ch 1%!4

30% caustic soda solution saturated with potass- ium permanganate. The determination is as follows: Firstly, all joints are made absolutely air- tight, and the tubing of the nitrometer must be of sufficient length to ensure that during manipu- lation no air enters the apparatus through the open tube. A weighed portion of the fabric to be analysed is wetted-out in flask A with distilled water and hydrochloric acid, and the rubber bung is insertted tightly in the neck of the flask. Tap E is opened, and the delivery tube of the tap funnel below the tap D is filled with distilled water to prevent an air-lock. Tap F is opened next and a steady stream of carbon dioxide passed from the Kipp through A for a t least 30 mins. Freedom from air is determined by passing the gas into C. If it is absorbed completely, only carbon dioxide is present in the apparatus.

A solution of sodium nitrite is placed next in funnel D, and allowed to run into flask A. The displaced carbon dioxide passes into C and is absorbed. The wool in A is allowed to diazotise for about 20 hrs. The nitrogen liberated is then swept into C by passing carbon dioxide through A, and next scrubbed well by passing the gas backwards and forwards from the burette to the nitrometer until no more is absorbed. The gas is passed into the nitrometer and measured at atmospheric pressure. The wool is removed from the flask, washed with water, then put back into A and a little distilled water added. Air is again displaced by carbon dioxide, a solution of cuprous chloride run into A from D, and the contents of A boiled gently until no more nitrogen is evolved and the gas dealt with as before.

The results are given in Table XVIII, 2.5 g. wool being used for each experiment.

TABLE XVIII OrIgJnul wool 0.556% Amino-nltrogen Wool boiled with wate;“ 0 6 8 5 3 ,, ,, Wool boiled with add ... 0649 /o ,, ,,

The increase in amino-nitrogen is only 0-087y0 and does not seem to be sufficient to account for the increased a e t y for the dye- acid. Speakman (loc. cit.) gives a higher value for amino-nitrogen, but it is probable that it is not a constant quantity. Assuming that all the amino-nitrogen combines with dye-acid, in the case of Indigo Carmine, 0.856 parts are equivalent to 9.23 parts of the dye, which-is rather more than the maximum absorption given in Table 11, but less than the figures given in Tables I V and IX.

ERRATA Column 1 (this Jour., 1934, 60, 42)for film (line 60)

andfilm (lines 61 & 52) read filement.

MANCHE!3TER SECTION Annual Conjoint Meeting of the Manchester

Section of the h t i t u t e of Chemistry, the Society of Chemical Industry, the Society of Dyers and

Colourists, and the Manchester Literary and Philosophical Society held a t the Collegc of Technology, Manchester, on 3rd November 1933, Dr. A. SCHEDLER in the chair.

Research in the Infra-Red SIR ROBERT ROBERTSON, K.B.E., F.R.S.

Short Sammury of Address Sir Robert introduced his subject by an

explanation of the position of the infra-red in relation to other regions of the spectrum. After discussing theoretical points, apparatus and technique, he described how infia-red rays had been applied in the elucidation of many problems, including atomic and molecular structure, the photographic recording of distant objects, the detection of erased cancellation marks on stamps, and the detection of certain pathological conditions, e.g. the disclosure of varicose veins, which could not be observed by the naked eye. In referring to the cxploration of the possibilities of infra-red for dctermining the most suitable dyes for fabrics to be worn in the tropics, Sir Robert expressed the opinion that satisfactory results in this field of investigation would not -be achieved until research wae carried out in a region of the spectrum farther from the visible portion. He remarked that infra-red radiation might prove valuable as a therapeutic agent, but much fundamental work would be necessary before its efficacy could be established.

The address, which was illuAtrated by diagrams and lantern slides, waR much appre- ciated by a large audience.

LONDON SECTION Meeting held at the Dyers’ Hall, on 3rd

November 1933, Mr. F. W. WALKER in the chair. A Debate entitled “That Chlorinated Aliphatic Hydrocarbons ate better than White Spirit for

Proposed by W. BROWN, M.Sc., A.I.C. and opposed by C. L. BIRD, M.Sc., A.I.C.

Mr. W. Brown (Proposer) said-Petroleum solvents have been used almost universally in dry-cleaning for close upon a century. During the last four years or so, however, there has been a revolution in dry-cleaning methods, owing mainly to the success with which chemical engineers have designed installations for the application of aliphatic chlorohydroc~rbons.

It is my confirmed opinion that compounds such as trichloroethylene, carbon tetrachloride, etc., are better than white spirit for dry-cleaning. Non-inJEammability-These new solvents pos-

sess the outstanding advantage of non-inflam- mability. It is this property that is responsible for the appearance of the shop-window install- ations and the “pulling aside of the veil”; which .hitherto has shrouded “dry-cleaning” in mystery as far as the man in the street is aoncerned .

*-Cleaning”

March 19341 BROWN V. BIRD. DEBATE-“DRY CLEANING” 73

The chlorohydrocarbons act also as highly- efficient fire-resisters or extinguishers. Although white spirit possesses the relatively high flash point of 100” F., and is certainly the safesb of the petroleum solvents, it must be conceded that it is a t a disadvantage compared with solvents showing no flash point at all. Even with its high flash point, white spirit is classified. by the Railway Companies as dangerously in- flammable. During dry-cleaning operations, there is a definite phase where the temperature is raised to many degrees above this flash point, so that white spirit is not free from danger throughout the whole process. Further, a t temperatures above its flash point, white spirit may cause both fire and explosion. The chlorinated hydrocarbons are absolutely free from such risks.

D. Stoddard, the chief advocate of white spirit or “Stoddard Solvent”, has declared that the chlorohydrocarbons possess a major advantage in non-inflammability and those experts, who are familiar with the restrictions imposed by the authorities on the use of petroleum solvents, fully appreciate the value of this advantage.

Better Solvents-The solvent range of the chlorohydrocarbons is much greater, and their solvent action more powerful and quicker in comparison with white Apirit. In my opinion, goods which have been treated in trichloro- ethylene or carbon tetrachloride are distinctly better than when treated in white spirit.

It is well-known that the mere treatment of goods in a grease solvent is not the whole of the dry-cleaning process. The most important part is that which follows the remova.1 of the greasy matters, i.e. “spotting or stain removal”. Experience with both trichloroethylene and carbon tetrachloride shows that the greasy matters are removed more thoroughly and the non-greasy matters more easily spotted out than is the case with the white spirit process. I am quite certain that the number of articles, which require to be “wetted out” entirely, is very much less when using the non-inflammable solvents. As spotting and wet-cleaning are expensive additional processes, it is claimed that the chlorohydrocarbons show an advantage in this respect. One non-inflammable solvent installa- tion is running satisfactorily on an extremely small amount of wet-cleaning, whereas the work of the same firm, when cleaned in white spirit, necessitated the wetting-out of about 25% of the total articles.

Every dry-cleaner knows the difficulty of cleaning the majority of white goods, especially when white grounds of patterns on woollens become grey or yellow. The chlorohydrocarbons do not cause “greying” or dulling of whites. The cleaning of silks with non-inflammable solvents has a remarkable clearing action on the colours. There appears to be an immediate freshness that is not obtained by any other process.

A3

Odour-At one time, dry-cleaning was asso- ciated with a certain odour, which was retained by the treated goods. This was caused, no doubt, by the presence of non-volatile residues in the cleaning spirit. Even a t the present time, it cannot be claimed that all brands of white spirit are immune from causing this defect, in spite of the vast improvements in the tech- nique of the petroleum industry during the last 25 years. Moreover, the high boiling points of many constituents of white spirit make it very difficult to ensure the removal of the last traces of the solvent without the use of high and pro- longed drying temperatures. Chlorohydrocar. bons, on the other hand, evaporate a t low temperatures, so that drying-out is easy, and even in the event of some solvent remaining in the articles, this would evaporate completely in a comparatively short time. “Odourless” clean. ing, therefore, can be guaranteed by the use of the new solvents.

Operating Coats-It is claimed that the use of chlorohydrocarbons tends to make operating costs lower than they are in the white spirit process. The distillation range for white spirit may lie between the limits of 90”-200” C. The Opposer uses a spirit in which 95% distils between 169” C. and 190” C. The highest b.p. in the range of chlorohydrocarbons is that possessed by perchloroethylene, viz. 119’ C., while the commoner solvents trichloroethylene and carbon tetrachloride boil a t 87” C. and 78” C. respectively. It has been stated that 1,620 B.Th.U. are required to evaporate 1 gall. white spirit from 70‘ F. to vapour at its final b.p., while 1,370 B.Th.U. are required for 1 gall. carbon tetrachloride. Trichloroethylene occu- pies a position between these two @urea.

It must be obvious that the cost of steam for drying-out and re-distillation purposes is very much less for the chlorinated hydrocarbons than for white spirit. This explains why non-in- flammable solvent installations can be seen working efficiently a t steam pressures below 10 lb. per sq. in., and in certain cases, even with exhaust steam. Solvent Consumption--The low consumption

figures of the chlorinated hydrocarbons as com- pared with those of white spirit are claimed also as an advantage.

The actual consumption of solvent depends, of course, upon many factors, particularly the type of appliance used, the care taken to prevent evaporation, and the attention paid to recovery. On the whole, the homogeneous nature and low b.p. of the chlorohydrocarbons enable a nearly theoretical recovery yield to be obtained. For commercial purposes, the solvent loss (or cost) per suit (as the standard article) is the vital figure. It is surprising to find that, starting with a handicap of 3 to 1 in cost per gall., these new solvents can compete with white spirit and in some cases show better figures. One non- inflammable solvent plant has claimed, e.g. that

74 BROWN V. BIRD. DEBATE-“DRY-CLEANING” [March 1934

after working over a period of three months. the solvent loss was only on the dry weight of goods cleaned. This is a solvent cost of about ad. per suit.

It is to be admitted that this is probably an isolated case, but it is indicative of what can be done.

There is one further point that needs to be stressed here, viz. the specific gravities of the various solvents must be taken into account in considering solvent consumption. Thus, for an equal yo loss by weight, the chlorinated hydro- carbons show approximately only half the volume of white spirit.

Mr. C. L. Bird (Opposer) said-White spirit is a mixture of p a r a h hydrocarbons of b.p. 15O0-2OO0 C. and flash point of about 100” F. It has no action on textiles or dyes, and it does not decompose under the action of sunlight, water, or metals. In practice, the losses due to evaporation are small, yet white spirit can be dried out of gar- ments without difiiculty. “Stoddard Solvent”, the standard American dry-cleaning solvent, has a &her final b.p. than the average white spirit.

A solvent of relatively high boiling range possesses the advantage that its flash point is raised to a temperature well above the normal and, in consequence, the solvent is no longer dangerously inflammable. Dry-cleaning was a dangerous process formerly, owing to the development of static electricity. The use of white spirit eliminates this danger.

The Proposer appears to hold the views that carbon tetrachloride has a definite toxic action, and that relatively low concentrations may cause lasting internal injury, e.g. the injury to the liver may be clearly marked, and like all chlorohydrocarbons it acts first as a narcotic, but the narcotic dose and the fatal dose are much nearer together than in the case of any other solvent.

In addition, carbon tetrachloride is unstable in presence of water and certain metals, e.g. iron. In consequence, machines intended for its use have to be constructed of some expensive material, e.g. Monel metal. It is stable to repeated distillation and storage, only when free from moisture. In presence of the latter and in contact with certain metals, it tends to decompose with the formation of some hydro- chloric acid and phosgene. These properties are disadvantages in dry-cleaning since moisture cannot be eliminated completely in the process.

Trichloroethylene is not as toxic as carbon tetrachloride. If it is used for cleaning articles by hand, however, it produces giddiness and nausea, ‘in marked contrast to white spirit.

An important property of trichloroethylene, from the point of view of the dry-cleaner, is its solvent action on certain dyes, particularly those for cellulose acetate rayon. The solvent action is slow a t the ordinary temperature, but rapid at elevated temperatures (cf. Bird, this JOUT., 1933, 49, 379). This defect does not

appear to be experienced in the small open-type plants, since, in this case, the period of cleaning is short and the drying is carried out cold. These plants are exceptional, however, because of their limitations. Where trichloroethylene is used on the large scale, the plant is always totally enclosed, and the garments come out of it both .clean and dry. The cleaning process is more prolonged, and the drying is always aided by heat. Thus, the garments are subjected to the action of hot trichloroethylene for a considerable period and it is here that the solvent action of trichloroethylene on dyes is demonstrated in practice.

Perchloroethylene is free from many of the defects possessed by carbon tetrachloride and trichloroethylene. A t its present price, however, it is not yet a practical proposition.

The totally enclosed plant, which both cleans and dries the garments, is by no means new. In fact, the “Barbe” machine is about 30 years old; but for ordinary dry-cleaning with petroleum solvents it is almost obsolete. This is not due to a growing desire for safety, since these machines can use even aviation petrol with perfect safety, but because it has been found that i t is best to use a machine especially designed for one purpose only. The multiple machine does a number of things and none of them really well.

In addition, the new machines seek, in many cases, to take advantage of modern develop- ments, such as-the centrifuge and the filter press. In consequence, there are wet residues to be removed at frequent intervals. Not only does this mean an appreciable loss in solvent, but, in the case of carbon tetrachloride, great danger to the health of the operator. The same thing applies to the still residues. Then again, there is the danger that the operator, when pressed for time, will open the machine before the work is completely dry, whereby he is exposed to the action of hot solvent vapours.

Every dry-cleaner gets articles to be cleaned which cannot be cleaned in a machine; these mud be cleaned by hand, e.g. silk lamp shades on wire frames, etc. Hand-brushing is an essential part of dry-cleaning. This cannot be carried out with trichloroethylene, and certainly not with carbon tetrachloride, if the health of the workmen is to be considered. In addition, hand-brushing with these solvents would entail high losses of solvent.

Then there is the problem of how to deal with garments containing rubber, in the form of dress protectors, rubber linings to pockets, and elastic bands. Garments of this kind are com- mon, but fortunately they can be cleaned with white spirit owing to the slow action of this solvent on rubber. On the other hand, rubber parts of garments are ruined if cleaning is done with chlorohydrocarbons.

Finally, it may be wid that, although the chlorohydrocarbons have their uses in dry- cleaning, their limitations are such that their

BROWN v. BIRD. DEBATE-“DRY CLEANING” 76 March 1934

adoption in large-scale practice is hedged round with restrictions, which are far more trying to the practical dry-cleaner than those encountered with white spirit. It is contended, therefore, that as an all-round dry-cleaning solvent, white spirit is far superior to the chlorinated hydro- carbons.

DISCUSSION Mr. E. J. Honess said that trichloroethylene

plants in Germany exercise only a secondary function in the dry-cleaning process. Benzine cleaning is still generally employed there.

Mr. D. O’Brien said that neither speaker had given definite results of the various dry-cleaning processes, i.e. the actual amount of water- brushing and of wet-cleaning required in each case.

Mr. F. R. Baker said that, according to the Opposer, cleaning in Burtol machines resulted in bad whites. This may be explained by the absence of friction in this method of cleaning.

Mr T. H. C. Barclay said that the Proposer had missed one point in favour of non-inflammable solvents. It was not necessary for him to prove that chlorohydrocarbons were better than white spirit. He needed only to prove that they were good cleaning solvents. Their use in shops and shop-windows aids in a general de-centralisation of the trade. Many cleaneru do not like this development, but the customer has to be con- sidered and there is no doubt that he likes to send his work for cleaning to firms who can do it quickly and efficiently. The Opposer had stressed the toxic nature of the new solvents, but the machines in use now were so completely enclosed that there was no reason to fear any toxic effect on the worker.

The Opposer said that it was not possible to clean everything in enclosed machines.

The Chairman (Mr. F. W. Walker) said that even if totally-enclosed plants were used with perfect safety during cleaning with carbon tetrachloride, there was a danger to health if filters had to be cleaned out. He believed that the only method available was to scrape the mud from the filter cloths before it was dry; the operation, therefore, was a danger- ous one, especially when carried out in an inadequately ventilated building. There was no danger during the operation of the plant, provided the doors were vapour-tight and the joints sealed properly.

Mr. Smith said that he had been working a plant for three years; the filter was cleaned in vacuo and the dirt brushed off without causing any smell. In the white spirit process, it wm necessary to brush linings with benzine soap, but not in the carbon tetrachloride process.

In reply to a question by the Opposer, Mr. Smith said that 2 or 3 washes could be carried out with the same supply of benzine, compared with 4 or A when using carbon tetrachloride,

Mr. R. B. Brown said that the main question at issue seemed to be whether or not it was a better proposition, commercially and practically, to clean with chlorohydrocarbons or with white spirit ?

The advent of the use of non-inflammable solvents had certainly brought the practice of dry-cleaning to the notice of the public, with considerable advantage to the whole industry.

The amount of spotting, cost of solvents, rapidity of the newer plants, frictional effects, the value of the non-inflammable solvents as an advertisement. e t a are amongst the factors that have to be considered before the question under discussion can be settled definitely.

The Opposer had stated previously (cf. this JOUT., 1933, 49, 316) that the variation in the effect by using different dry-cleaning maohines could be very much greater than that produced by the ingredients of the bath, time, tempera- ture, etc. which were used in laboratory experiments, so that the results of the latter were not the same as those obtained on the practical scale. The Proposer and the Opposer in this debate had made out good cases, but it was impossible to say with certainty that one solvent was better than another.

Mr. E. Beeley said that in a pamphlet issued by one maker of solvents, it is stated that tri- chloroethylene is six times as eacient as benzine. As regards the question of toxicity, it was stated recently in this Journal that any toxic effect caused by trichloroethylene is temporary and in no case leads to permanent injury. The Opposer’s case seems to resolve itself chiefly into a question of toxicity and the dissolution of dyes on cellulose acetate rayon.

Mr. D. Christophemon said that he had not seen on0 case of nausea or illness among men engaged in the manufacture of carbon tetra- chloride during a period of 12 months This is a fact of importance, since no one is in closer contact with carbon tetrachloride than the men who make it. He wished also to refute the statement that phosgene is formed sometimes. The Opposer had stated that hydrochloric acid was formed under suitable conditions. If it were produced to a reasonable extent, the goods would be damaged and it was necessary, there- fore, to judge b;s results. No complaints of any type concerning the formation of acid in plants had been received by his firm.

The Chairman asked if no phosgene were formed during the recovery period in the plant ?

Mr. Christopherson said that the gae had never been found.

The Opposer qid that in a lecture given by the Proposer last year, he had exhibited a corroded aluminium fitting from a cleaning plant; presumably the corrosion was due to hydrochloric acid.

Mr. R. B. Brown-said that the Proposer’s views on toxicity were supported by the 1932

76 BROWN V. BIRD. DEBATE-“DRY CLEANING” [March 1934

report of the Chief Inspector of Factories, an extract from which appeared recently in this Journal (1933, 49, 325). It is stated definitely that no serious case of toxicity occurred in the year covered by the report.

The Chairman said that he knew of a case of damage to the optic nerve by trichloroethylene. Some people can work with trichloroethylene for years, however, without harmful effects, but others have to discontinue after a week.

With regard to the formation of acid, he had noticed that after 6 months’ operation, an enclosed carbon tetrachloride plant gave a greenish coloured distillate (mainly carbon tetrachloride, but also moisture) ; this seemed to indicate the presence of dissolved copper, which in turn indicated the formation of acid.

Mr. F. G . Newbury said that he had had experience of both types of solvents and em- phatically supported the views of the Opposer. Some very dirty suits were cut in two; one-half waR cleaned in trichloroethylene and the other in white spirit. There was not the slightest difference. Not a single water-soluble stain was removed by the trichloroethylene. When totally-enclosed machines are used as cleaners, extractors, and drying-rooms a t very low tem- peratures, the “capacity” nearly vanishes. He considered that the proposal to clean on a large scale with trichloroethylene was not a sound one. The question of solvent property is not so important as the speed with which the dirt is removed from the machine. If suitable means were taken to remove the dirt as quickly as possible when using carbon tetrachloride, there would be little to choose between the solvents, although goods cleaned with white spirit were distinguished easily by their softer handle.

Mr. Baker asked if both halves of the suit were cleaned in the same type of machine ?

Mr. Newbury said that in one experiment, the suits were cleaned first in white spirit in a large vacuum-type machine and then split; one half was cleaned next in trichloroethylene in a small open-type machine. No improvement was effected.

Mr. J. C. Sowry said that he had found tri- chloroethylene to be a satisfactoty cleaning agent, and Mr. Newbury commented on the absence of dry-cleaning standards.

The Proposer said that his task had been a difficult one, partly bccause the Opposer had confined his remarks to white spirit, whereas he had to defend several solvents. It might have been wiser to have said that the new solvents were as good as white spirit and that would have been quite satisfactory. He was convinced, however, that they were better. The Opposer had stressed the property of non-inflammability. White spirit, it is true, is not quite as dangerous as other solvents, but i t is not free from the risk involved by accumulation of static electricity,

-

when operating at a temperature higher than the flash point. It would appear from the general discussion that the whole problem could be summed up as follows-

The risk of fire and explosion in one case, and toxicity and solvent action on certain dyes in the other case. The whole question of toxicity needed to be re-considered.

The Opposer had referred to some previous statements of his about toxicity, but he had in- tended merely to point out that the new solvents were toxic under certain circumstances. If there were no reports of any cases of serious injury in the plants operating last year, it would seem that this aspect of the discussion need not be pursued further.

As regards the production of acid, it was a well- known fact that carbon tetrachloride is un- stable in the presence of moisture and certain metals, and this knowledge was used to avoid con- ditions which result in the formation of acid. The corroded aluminium coupling which had been shown on a former occasion was intended to demonstrate the necessity of understanding the properties of the solvent. Experience showed that there had never been any instance yet of the production of acid in the goods during treatment. It was not suggested that work should be undertaken in the open with the chloro- hydrocarbons. Even with the Burtol apparatus, however, which is the most open plant on the market, there has not yet been a case of serious toxicity.

The defect of colour-bleeding is concerned with a proper understanding of the properties of the solvent. When the temperature rises in dry- ing in enclosed apparatus, there is a certain risk that the solvent action of trichloroethylene will remove the colour from cellulose acetate rayon. If there is bleeding, it is very slight and scarcely noticeable after the operation. As regards the action of solvents on rubber, it is doubtful if it can be cleaned, with impunity, with any “spirit” in the dry-cleaning range.

Mr. Newbury had referred to the compara- tively softer feel of goods cleaned with white spirit; this result supports the claim that the non-inflammable solvents have a greater solvent action than white spirit, i.e. the natural grease, e t a is removed more completely and the wool becomes harsh. No solvent is immune from action of this kind; it has always been one of the criticisms against dry-cleaning and some cleaners used to add lanoline in the last rinse to replace the natural fat.

The proposition was put to the meeting when twelve members supported the motion and twelve opposed it. A number abstained from voting. The Chairman then gave his casting vote in favour of white spirit, but expressed the view that there was a field for both types of solvent,