T H E ROTATION OF MELTING ICE S U S P E N D E D IN BENZINE.*

BY

H. B. HACHEY, B.Sc.

A PAPER written by A. Artom concerning the formation of hail was published on June 18, I922, in, the Accad. Lincei. Atti (31 i, pp. 513-518). In discussing this paper, Science Abstracts (No. 3o6, June 25, I923) makes the following remarks: " The electrical conditions for the formation of hail are discussed. This takes place in a medium rendered feebly conducting by ionization in which occur insulating bodies, such as the nuclei of the hail. The ionization is due (i) to the emissions from the sun. regarded as an incandescent body at a high temperature sending out cor- puscles negatively electrified, and (ii) to the action of the ultra- violet rays. Hail is usually seen in the hottest part of the day when the ionization by ultra-violet rays is strongest. Hail is formed frequently between rain clouds with high electric charges, and water vapor in the presence of ice has the property of feeble electric conductivity. In these circumstances the electric field causes an action of rotation which acts on the small drops of water. A piece of ice suspended in. benzol begins to rotate and continues this motion as long as the suspending thread permits. Such a rotating mass forms a solid of revolution and such are seen in the case of hail. Helicoidal forms due to the additional action of gravity are also observed."

It is quite improbable that such a theory of the formation of hail could replace the precise explanation of Simpson., which is generally accepted at the present time. ttowever, the writer's statement that a piece of ice suspended in benzol begins to rotate and continues this motion as long as the suspending thread per- mits, led to an in.vestigation to determine :

(i) Whether ice does rotate when suspended in benzol; (ii) Whether this rotation is a surface effect or a volume

effect ; (iii) Whether it was true of liquids other than benzol.

* Communicated by Dr. A. S. Eve, Director of Physics, McGill University, and Associate Editor of this JOURNAL.

825

826 H . B . Haci-Iev. [J.F.I.

It was first necessary to obtain a suspension thread that would hold the portion of ice to be suspended and yet offer very little resistance to a slight turning moment. Again it was necessary to make certain that all twist was taken out of the suspension thread so that the results obtained would be due to the effects of ice in benzol.

Silk fibre was chosen as the suspension thread, and by attaching a weight (approximately equal to that of the ice) and leaving it in suspen.sion over night, all twist in the thread was taken out. The ice was suspended in benzol whose temperature was about 2o ° C., and it was seen that the ice revolved until the suspension thread stopped the motion. This was repeated with the benzol at temperatures ranging from 2o ° C. to - I o ° C. and it was seen that the speed of revolution decreased with the lowering of the tem- perature until it reached the point (somewhere between 5 ° C. and o ° C.) where all motion ceased or was practically negligible. When a temperature of - I o ° was used, there was absolutely no motion of revolution noticeable. Then the height of the ice from the bottom of the vessel was varied and it was seen that the speed of revolution varied with the height of the ice above the bottom of the vessel, i.e., the greater the height the greater was the speed of revolution, always, of course, provided that a portion of the ice was under the surface. Again, the speed depended to a certain extent upon the amount of ice immersed, for the revolv- ing motion was much more rapid when the ice was completely immersed than when it was only partially immersed (keeping the height of the ice above the bottom of the vessel constant). It was also noticed that the direction of rotation was not constant and that when the same piece of ice was inverted it did not always turn in the opposite direction.

All through this investigation it was apparent that when the ice had motion of revolution (when the temperature of benzol was above o ° C.) a steady stream of water flowed from the ice to the bottom of the vessel containing the benzol. As soon as large drops, which'also formed on the lower end of the ice, gave way and were precipitated to the bottom of the vessel, the rotation of the ice was accelerated.

The experiment was repeated with water and also with gaso- line. When ice wa, s suspended in water there was absolutely no motion of revolution noticeable ; but when the ice was suspended in

June, 1924.1 ROTATION OF MELTING ICE. 82 7

gasoline the results obtained were similar to those obtained with benzol.

From the results obtained the natural conclusion is : (i) That ice when suspended in benzol does rotate. (ii) That the speed of rotation decreases as the temperature

of the benzol is lowered and all rotatiorr ceases when the benzol is at the temperature of o ° C.

(iii) The rotation also takes place when gasoline is used, but in the case of water the ice did not rotate.

(iv) That the rotation, is probably due to the downward flow of the denser melted water producing a torque owing to its irregu- lar motion reacting on the ice, particularly when the surrounding medium is much less dense.

Use of Diphenylamine as an Indicator in the Volumetric Determination of Iron.--J. KNOP (lout. Am. Chem. Soc., 1924, 46, 263-269) recommends the use of diphenylamine sulphate as an internal indicator for the titration of ferrous salts with standard potassium dichromate solution. Three drops of a I per cent. solution of diphenylamine in concentrated sulphuric acid are used as an indicator in each titration. The end-point occurs when the addition of one drop of the potassium dichromate solution produces an intense violet-blue color, unchanged on further addition of that reagent. The method may be applied to ferric salts, which have been reduced by stannous chloride followed by addition of mercuric chloride. This method also permits back-titration. J . S . H .

Mercury as an Industrial Poison.mJ. A. TURNER, Of the United States Public Health Service (Pub. Health Rep., i924, 39, 329-341), has studied several cases of mercurial poisoning, due to the passage of mercury vapor into the atmosphere from the mercury gaps in induc- tion furnaces. He finds that the signs and symptoms of mercurial poisoning are produced in man by exposure, for several hours daily during a period of two or three months, to an atmosphere containing as small a quantity as 0.02 milligram of mercury per cubic foot of air. If the daily period of exposure be between three and five hours, the daily absorption of mercury ranges between o.771 and 1.285 milli- grams. The symptoms develop chiefly in the mouth and gastro- intestinal tract; the blood and urine are not affected. The mercury vapor from the furnaces condenses, for dust from the furnace room contained from I to 3 per cent. of metaUic mercury. Poisoning of this nature is best prevented by inclosing all apparatus in which mercury is used, and by conveying the fumes away from the worker's face so that it will be impossible for him to inhale them. J . S . H .