connected with the Boiling of Liquids, 439 



(3) Porous bodies, such as charcoal, coke, the various woods, 

 meerschaum, chalk, &c. ; these act as permanent nuclei. (4) So- 

 luble substances, such as sugar, gamboge, &c, which act as 

 nuclei by diminishing adhesion between the gas or vapour and 

 the water. A body in Class 1 is said to be chemically unclean 

 when it is contaminated by a body in Class 2. 



M. Gernez regards these bodies merely as vehicles for convey- 

 ing air into the body of the liquid ; he maintains that such bodies 

 have no nuclear action per se, that porous bodies, such as char- 

 coal, and resinous and fatty bodies, such as shellac, stearine, &c, 

 have no specific action, because when deprived of air by repeated 

 boiling they become inactive. I have not been able to deprive 

 fragments of cocoa-nut-shell charcoal of their nuclear character, 

 although employed in distillations for days and weeks together. 

 My first paper contains some numerical results showing how 

 singularly efficacious cocoa-nut-shell charcoal is in separating 

 vapour from boiling liquids and increasing the amount of the 

 distillate ; and on this account the use of porous nuclei in such 

 operations is strongly recommended. M. Gernez also, in his 

 practical applications at the end of his memoir, gives similar 

 advice. 



I felt the point in dispute to be of such importance that I re- 

 peated the directions of M. Gernez, namely to boil what I call 

 a permanent nucleus a number of times at short intervals. For 

 this purpose I selected a fragment of cocoa-nut-shell charcoal. 

 Mr. Hunter has taught us* how powerfully and rapidly this 

 substance absorbs vapours at various high temperatures — such 

 as 255*4 times its volume of the vapour of a mixture of 10 cubic 

 centims. of absolute alcohol and 30 cubic centims. of water, 150 

 times its volume of methylic alcohol, 261*8 of a mixture of 10 

 cubic centims. of methylic alcohol and 20 cubic centims. of 

 water, 117 of bisulphide of carbon, 87 of ether, 116 of acetic 

 ether. These measurements were all taken at 100° C. The 

 mean of several observations for vapour of water gave 43*9 vo- 

 lumes absorbed at 127° C. Accordingly water was boiled over 

 the flame of a spirit-lamp in a clean tube in the presence of a 

 triangular fragment of cocoa-nut-shell charcoal. It was boiled 

 eleven times, at intervals of rather more than five minutes, as 

 M. Gernez directs. While the tube was still warm it was put 

 under the receiver of an air-pump ; and the exhaustion had not 

 proceeded far when a violent burst of vapour from the charcoal 

 turned out about one third of the water from the tube. The 

 tube was again boiled, plugged with cotton-wool, and left for 

 about three hours. It was again placed under the receiver, and 



* Journal of the Chemical Society, vol. hi. 1865, p. 215. See also vols. 

 v, & vi. 



