April 15, 1930 I S D r S T R I A L A,\-D ESGIiVEERIiVG CHEMISTRY 177

Device for Rapid Estimation of the Density of Small Amounts of Solids‘

Earle R. Caley

DEPARTME\I OF CHEMISTRY, P R I S C E T O X U X I V E R S I T Y , P R I Z C E I O N , N. J.

N CERTAIN investigations it is desirable to determine rapidly the approximate density or specific gravity of small amounts of solids the available weight of which

renders the employment of the usual means of making such eqtimations impracticable. The simple instrunient shown in the illustration, which might be termed a “microdensimeter,” has been found useful in such cases and is particularly recom- mended as an aid in the rapid identification of fragments of material.

The principle involved in the operation of this device is elementary. The narroK graduated tube is partially fillell n i t h a suitable liquid and the level of the fluid is carefully read with the aid of a reading microscope. Then a weighed portion of the coarsely powdered material is introduced into the tube and the rise of the liquid level in divisions is noted. Since the i.olume represented by each division is known from a careful calibration, the volume of the sample is thus given. and this value divided into the weight of the sample give,., of course, the desired density. Khile the principle involved is quite simple, it vas found that satisfactory results are obtained only by careful attention to the proper construction of the instrument and the method of using it.

Description of 3Iicrodensimeter

I

This instrunient is easily constructed from glass tubing, but it is essential that the tubing selected for the narrow tube be of quite uniform bore and care must be exercised that the uniformity of the part to be graduated is not altered in the operations of closing the tube and forming the upper portion. It is also important that the internal diameter of the gradu- ated tube shall not exceed 2.50 mm. or be smaller than 2.00 nim. A larger diameter means loss of accuracy due to the correspondingly smaller changes in the level of the liquid for a given volume of the solid, while a smaller diameter leads to difficulties due to the inclusion of air bubbles in the tube when it is being filled with liquid. Tubes of smaller diameter than 2.00 mm. also render difficult the ready introduction and removal of the coarse particles and powders that are used for density determinations by this method. The enlarged portion of the tube, which allows the sample to be readily introduced into the smaller part, should be from 1.5 to 2.0 em. in diameter and about t-&e as long. It should taper gradually and smoothly into the narrow tube and should have its upper portion so formed that it may be tightly closed with a rubber or glass stopper.

A suitable length of the narrow tube is arbitrarily gradu- ated into a number of divisions spaced not more than 1.0mm. apart. These graduations must be spaced very evenly and should be etched in lightly to increase the accuracy in reading. The glass part of the instrument used in obtaining the values shown in the tables had a total height of 13.4 cm. The length of the narrow tube was 9.5 em., the total distance occupied by the 100 divisions being 7.3 em. The external diameter of the graduated part of the tube was 6.0 mm. and the in- ternal diameter 2.33 mm.

The finished tube is provided with a well-fitting glass or rubber stopper and a base that permits the ready removal

1 Received December 30, 1929

of the tube for cleaning and inspection. The completed instrument is calibrated with distilled water at 20” C. in the usual manner. The water for calibrating is most con- veniently introduced by means of a pipet with a drawn-out capillary end. The accurate reading of the liquid level in the tube is most conveniently clone by inearis of a 25-50 power reading niicroscope proi idecl with cross hairs and arranged to slide vertically on an upright stand. With this accessory there is little difficulty in reading tenths of a division on the tube. Less satisfactory reaults are obtained by using a reading lens oning to the difficulty of avoiding errors due to parallax.

Displacement Liquid

It was found impracticable to employ water as a confining liquid in this instrument, since its high suface tension caused gross errors due to the inclusion of minute air bubbles in the tube and between particles of the solid sample. The most satisfactory displacement liquid is ethyl ether. K i t h this fluid there is rarely any air bubble formation either in the tube or between fragments of the sample and any minute air bubbles present are readily removed b y t a p p i n g the tube gently. Ethyl ether is also of great practical adran- tage in making a series of determina- tions, since successive samples are readily remored from the tube by shaking, and the remaining film of ether evaporates rapidly leaving a clean, dry tube ready for another estimation. Ether further permits the direct estimation of the density of most water soluble substances by means of this method. Alcohol and other liquids of low surface tension may be substituted, but in general these are less satisfactory and should be used only in cases where the material examined is soluble in ether. The only disadvan- tage in the w e of ether lies in its vola- tility, but the error arising from this source may be made negligible by proper manipulation.

S e v e r a l experiments demonstrated that it was necessary to use a stoppered tube in order to prevent undue error from the evaporation of the ether even from such a small surface as is exposed in the narrow tube of this instrument. These experiments were conducted by filling the clean, dry tube with ether to dif- ferent points and making successive readings a t 5-minute intervals. Table I shows the increased rate of evapora- tion from a n open tube as compared with that from a closed tube, and it also shows how the rate of evaporation decreases as the length of empty tube above the surface of the liquid is increased. It will also be noted that in the experi- ment with the closed tube a certain time was required to obtain equilibrium, as might be expected, The latter experi-

Microdensimeter

inent also denionstrates that when a stoppered and partially filled tube is used t,he rate of evaporation is too small to effect two successive readings that occur about one iniiuite apart, which is the case in an actual tleterniination. Ki th lehb volatile liquids. such as alcohol and benzeiie, it was f ( ~ u i i t i that the rate of evaporation in open tube.? of th i i mia l l c n w section is negligible for the purposes of this iiietliod.

Table I-Rate of Evaporation of Ethyl Ether from the Microdensime- ter Tube under Different Conditions

(Temperature, 20' C.1 ELAPSED OPEX TVBE OPES TUBE S T O P P E R E ~ TL.BE:

TIXE SE.AKLY FILLED HALF FILLED IIALF F I L I . ~ ~ M i n u l e s Reailinn Readins Readin<

5 96 1 3 9 0 ;16 i 10 95 1 B8 4 36 2 15 94 4 58 1 0 20 93 7 n7 8 25 92 9 s i . 4 30 92 0 a7 0 3 35 91 2 56 6 (1 40 90 6 S 45 .-A 6

:

Procedure for Density Determination

The solid material must first br reduced to particlw ( I F suitable size for introduction into the instruriient. Tht, method used will vary with the material to he examined. In the case of minerals and crystalline substance; a coiir-Pnieiit procedure is to crush the niaterial in an agate or steel mortar and select suitable fragiiieiits with a forceps as the sample i b progressively reduced to srrialler particles. The he5t results are obtained when particle.; ranging from 0.3 to 1 ..j 111111. in diameter are taken. In the case of metal; or alloys fine clippings or coarse filings niay be taken from the saniplc,

Sole-This method i i not adapted to determining the density of fine powders since errors ariie from the inclusion of minute air spaces between the particles of powder and there is often difficulty in introducing ruch ponders into the tube due to the tendency of the material to collect a t thc meniscus. It is obvious tha t the density of deliquescent and sticky s u b stances cannot be determined by this method owing to their tendency to adhere to the walls of the small tube.

has been prepared. the tube i h filled about e ether. by mean. of a sniall pipet. So

iiicluded in t'he tube if this oppration i\ properly performed. but if any are trapped gentle tapping v-ill caure them to rise to the t'op. The instrunieiit is then Ptoppered while the sample is weighed out. Tlir weight to tie taken will depend upon the aiiioui and the probable density of the sub sample of from 0.0500 to 0.1000 gram 1 riietallic materiak, while a saniple of from 0.2000 to u.:jooo gram is best for nietals of high density and their alloys. rseful results in either case, howel-er. can be obtainctl with smaller samples. As soon as the sample has heen ivrighed out,. the liquid levrl is read to the nearest tenth of a division with the reading microscope. Then the stopper is renioved from the tube and the sample is introduced. after whic31i thc tube is immediately restoppered. The instruniriit is then gently tapped several times to bring all of the aaniple into iiie liquid and to cause any minute air bubbles that may he present to rise to the surface of the ether. Thr recontl reading of the liquid level is made immediately. The interval between the two readings of the liquid level should not tx longer than one minute. d simple calculation then serves to give the required density.

There is no need to apply a teiiiperature correct'ion for the expansion of the glass tube over the ordinary range of room temperatures, since the error that might arise from this source is small compared wit>h the other errors of the method. When liquids other than ether are used, care mu5t be taken that sufficient, time is allowed for the surface of the tube above the meniscus to dry completely before introducing the sample.

Table 11-Rapid Estimation of Densities of Several Son-Metallic Substances Using Small Samples

DIFFERE\CE

Gram cc. P U R E POTASSIL'M CIILORIDfi>

0 129 i "1 2 0 0657 1 9 s 0 1014 16 A 0 031.5 1 97

0 OR13 I4 , 0 0456 2 00 0 1014 16 2 0 051% 1 9s

A V . 1 R Y 1 !l!l I ' IRE SOD1l.M ClII.OKIDE

0 1111 16 6 0 051,; 2 1s 0 1071 1% O 0 0496 2 16 (1 1002 15 (1 0 0463 2 . 13 (1 0913 13.6 0.04'22 2 16

XI.. 2 , 16 2 1 i ICEL.AND S P A K

Table 111-Rapid Estimation of Densities of Several Metals Usin, Small Samples

P U R E .\LL'hlIhUM \VIRE 0 l U 3 i 12 3 0.0388 2 6 i

12 .i 0 0388 2 67 12 4 0 0384 2 70 12 : 0 0388 2 67

0 3116 14 2 0,0440 7 08 0 3161 11 3 0 0443 7 . 1 4 0 2971 13 6 0 0422 i . 0 4

7 2'' 0 2 7 3 2 1' 3 0 0381 0 343" 13 8 0.0490 7 04

hr 7 . 10 i 12 P U R E COPPER \?IRE

0 3224 11 i n 0363 8 88 11 9 0 0369 8 i 4 11 8 0 0366 8 81 11 8 0 0366 8 81

(1 2733 9 8 0 0304 Av 8 81

8 99 8 8 2

Table IV--Rapid Estimation of Densities of Various Substances Csing Unusually Small Samples

S A M P L E TAKES G r a m

0 0656 0 0606 0 0326 0 O?i9

O 0,584 0 0 5 i %

0 . 0 2 i 6 I) 0413

n 0316 0.0405 0 0310 0 0202

0 0383

0 ,0279

DIFFEREXCE

R E A D I N G S V01,rruE F o r s u CC.

B E T W E E S S C A L E DISPLACED D E S S I T V

PI'RE P O T A S S I U M CHLORIDE 10 B 0.0326 2 01 9 7 0 0301 2 01 ,-r 3 0 0164 1 99 4 3 0 0140 1 99

A\'. 2 . 00

8 9 0.0276 2 . 1 % 8 6 0 0267 2 . 1 4 6 1 0 0189 2 . 1 9 4 . 1 0 0127 2 . 1 7

h v . 2 .16

6 3 0.0183 2 . 7 9 4 . 8 0,0149 2 .72

0 0118 2 63 ;: 0 0074 2 73 A v . 2 72

4 7 0.0146 2 64 4 7 0 0146 2 64 3 4 0.0103 2 66 3 5 0 0109 2 . 5 6

.I\.. 2 . 63

PL-RE S O D I U M C H L O R I D E

I C E L A N D S P A R

P U R E A L U M I S U M \\'IRE

Results

The results obtained on rarious subitances by the above procedure are shown in Tables I1 to IV. These are all of the values obtained in series of determinations and are not selected results. The d u e s found by the pycnometer Inethod were determined a t 20" C. on large samples of the

same inaterial as u-ed for the other deteriniiiatioiiz in each ca-e Each dir iiiori of the particular iiiicrodeii.inieter iiie[l for thiq series of dcterniinations repre-eiited a volmne of 0 0031 nil. a t 20” C. The actual deteriiiiiiatioii. by the rapid method nere macle a t iooiii teiiiperatuie. that rarigetl iroiii 20” to 25” C

The be.t re*iilti n ere obtained n hen the cliffeicwce betn eeii the t n o reading’s amounted to more than teii *calr clivi~ioii. Thi. i5 due to the fact that the effect of any erior 111 reacliiig tlie tli.placetl volume i. then a. mailer percentage of the total T ulunie than would be the ca4e n here a smaller volume i\

di.placetl. If po5qible. therefore. \aiiiple- large enough to tli-plac~ a volume of liqiiid corre.polidiiir: to a t lea-t ten

divisioiis of the scale ~Iiould be taken. I--el‘ul results:. lion.- ever, caii he obtained with iiiuch m a l l t ~ iaiiiple., a,< t l i c ~ values in Table IT’ $how. 111 the-e caac- thc results of in- dividual deteriiiiriatioii.: are ieeii to x-ary iiiore from thc truc value than do tho>e where a larger voliiiiic. ( J F liquid .ic dis- placed. h t the average value of a ,series of such (1Pteriiiiii:x- tioris is. in griieral, quite satisfactory.

. I d e froin tlie sinal1 ainount of saiiiple rrqiiircd for tleiicity tleteriiiiiiatioiis by thir method. another arl~.aiii-age lirs iii tlie rapidity by JTliicli the results may 1~ o1)taiiied. -1 siiiglr tlrteriiiiiiatioii may be made in from 3 to 10 iiiiitutes iiicliidiiig all operation.. and a Gerie. Of (l(,t~riiiiiiati~~iis can bc iiiatlo Jritli siiiiilar rapidity.

Relay for Use in Regulatory Circuits’ L. G . Wesson

S c.lectroinagiietic rela iii which tlie operatiiig circuit is automaticallj interrupted and in v-Iiicli A uiidesirahle sparking is prevented. has been developetl

a d used in therinoregulatioii iii this lahoratory for tlie past year. T T V ~ dry cells only are iiecesqary for operating thc 1~1ay and n-ill last for months viithout attelltion. &ice current i - drawn from the cells only during tlie time that tlie relay ariii iiior-es froin one position to the other. The sparking that occurs a t the hreak of the circuit in tlieriiioreRulator*. ctc.. which may be used i n connection with this aiid certaiii other forms of relays,, is the cause of iiiuch difficulty iii opera-

Figure 1-Electromagnetic Relay

tioii because of the corrosion or sticking of tlie iiietal tips OK osidation of the mercury surface of the thermoregulator. 111 the relay to be described this difficulty is a\-oitled, since the actual break of the circuit takes place a t ai1 insensitive juiiction in the relay, iiistead of a t a sensitive junction in the t hermoregulator.

The relatively heavy currents that often are sn-itched oii

aiid off by a relay are a troublesome feature of regulatory circuits becaure of sparking. This difficulty is avoided. as

-pes of regulatory circuits hrought out in 1 by the-use of a mercury switch2 iii coli-

By iiieaiis of this switch currents as iiectioii with this relay. 1 Received October 21, 1929. 2 This switch consists of a closed glass tube into which are sealed con^

tacts of special material. It contains a quantity of mercury which, when the tnhe is tilted, will make or break the circuit. With the mercury switch there is no open arcing. oxidation, or corrosion. The switch contains inert gases hermetically sealed within the tube which stifle the arc. Different types of mercury switches are available, and are designed to carry loads from

Description of Relay

The relay (Figure I ) c o i i r i - t i esxeiitially of t w J electroiiiag.iiet~,:~ .\I, M’> eacli acting on m e elid of ail

approsiinatelp balanced ami. .-I, .I I ,

(wrying a inercury switch, A‘. T\vo wires, TT7, lf7’, which are iiisulatetl From the arm aiid which are provided with platiiium tips, are so arranged that t l iq- can he lo~veretl by iiieaiis

e ~ s , R. R’. into cups of iiiercury.? F . F’ , one of n-hicli is IF- 101~- each elid of tlie ann . (-4 layer i d

liquid petrolatuin protects the mer- (wry h i i i corrosion.) =Idjustnient ( ~ f the wires is iiiade s o that ~ ~ h i l e the wire a t oiie eiid of the arin dips well iiito the iiiercury when the corrc- spoiidiiig elid of the arm is dowii, it just, clear* the surface oi the inerciiry when that end of tlie arm is in tlie raised positioii. The curreiit fro111 tlie dry cells passes through tlie v-ire 11-liicli is in contact with the iiier- cury a.3 so011 as the cirruit is closed a t t l i e s e n s i t i v e j u i i c t ~ i o n of the thermoregulator, arid passes thence througli a n electromagnet, a t t l ie o t h e r elid of the ami. The magnet pulls down that elid of the ariii, -1 I , and while doing so lifts the wire from the mercury a t the eiid .-l of the ami. and thus breaks tlie cir- cuit. -1s the relay starids iion, the circuit is closed through the wire,

Figure 2-Toluene Type of Thermoregulator

T i - ’ , aiid the correspoiidiiig electrciiiiagiirt, .V, rxcept ~ I X

tlie open junction i n the therinoregulatc,r. Wheii this open jiuiction of the therinoregulator i,? closed hy change of teiii-

1 to 10 amperes a t 110 roltij or 1 to $5 amperes a t 220 volts. are sAd by the Llercoid Corp , 564 \Vest Adami St . . Chicago. Ill.

J . H. Bunnell 8: Co , 32 Park Place, S e w I-ork, S . I’.

hlercury switches

3 Sounder magnet4, ruhher-covered. 4 ohms, Catalog 30, 1-0. 6203,