obtained from Caoutchouc by Distillation. 481 



By this we learn that the evaporation from No. 4 is exceed- 

 ingly more than that from any of the others. 



The most remarkable circumstance relating to this evapo- 

 ration from liquor No. 4 remains to be noticed : it is one that 

 distinguishes it from the vapour of every other liquid that I 

 have yet examined. The vapours from aether, alcohol, sul- 

 phuret of carbon, &c., are rapidly absorbed by water, in the 

 same manner as are muriatic acid and ammoniacal gases ; 

 but tlie vapour from caoutchouc liquor highly rectified as 

 No. 4, may be passed through water repeatedly without any 

 sensible diminution or alteration of its quantity; at least the 

 action is not more than on olefiant gas. The way to charge a 

 quantity of air widi vapour of any kind is to fill a phial with 

 mercury, let in the proposed air till the phial is half full, then 

 inverting it carefully, drop in a little of the liquid to be eva- 

 porated, and immediately after again invert the phial over 

 mercurv in the trough. The vapour then expands the air, 

 and in a short time the maximum of expansion is produced. 

 The mixture of air and vapour may then be used for any pur- 

 pose over mercury. In the case of aather, however, a mercu- 

 rial apparatus is not absolutely necessary; in a narrow tube 

 aether may be turned up through water, and, if sufficient to 

 form a thin stratum over the surface of the water in the tube, 

 the aether vapour will rise into the air, and be defended from 

 the water by the stratum of the liquid : in this way the mixture 

 of air and vapour may be confined in repose for a month. 



In regard to the vapour from caoutchouc liquor No. 4, no 

 such precaution is necessary. I take a graduated jar of 4 or 5 

 inches diameter ; and having filled it with water, I let in 60 

 cubic inches of air, and turn the cock so as to confine it. I 

 then put 20 or 30 water grain measures of the liquor into a 

 tube and turn it into the water in the jar, through which it 

 ascends to the surface and instantly spreads over it a thin film 

 of an oily appearance. This film by degrees almost disap- 

 pears ; at the same time the air gradually expands, and in about 

 twenty minutes acquires its full expansion, becoming about 90 

 inches in a temperature between 60° and 70°. It will remain 

 for days in this state, and there will be no change of volume 

 unless there be a change of pressure or temperature of the 

 atmosphere. 



This permanency of the vapour over the water affords an 

 admirable facility for finding its specific gravity. Let 60 cu- 

 bic inches of common air be expanded by vapour, suppose to 

 90 ; then, exhausting a flask and letting in a given number of 

 inches of the mixture and weighing it, we shall have data to 

 find the weight of the vapour, knowing previously that of 



Third Series. Vol.9. No. .57. Suppl. Dec. 1836. 3M 



