Polytechnic Association Proceebings, 573 



the only instance hitherto noticed of a diminution of bulk, is the 

 mixture of chloroform and bisulphide of carbon {eralid and ares); 

 a decrease of heat takes place at the moment of union. 



3. Aside from the loss of heat resulting from a change of volume, 

 there exists a cause which absorbs heat equal, and sometimes greater 

 in amount than that given out by the combination of liquids. This 

 cause, perhaps, may proceed from the separation of homogeneous 

 particles necessary for the diffusion of the liquids. 



ACTION OF LIGHT ON IODIDE OF LEAD. 



M. Schmidt, in the Bibliotheque UniverseUe de Geneve, arrives 

 at the following conclusions by experimenting with paper coated 

 with a mixture of iodide of lead [plubamev) and starch: 



1. The iodide, when in a perfectly dry condition, remains unal- 

 tered when exposed to light. 



2. "When kept in a moist state, it is decomposed by light. 



3. In order to effect its decomposition, the iodide must remain in 

 contact with the atmosphere. Iodide of lead mixed with starch, or 

 with an alcoholic solution of gum guaiacum, remains perfectly unal- 

 tered when exposed to light in vacuo, but changes to a bluish color 

 immediately on air being admitted. 



4. Pure iodide of lead, in a moist state, becomes decomposed in 

 appreciable quantities by time; it assumes a more transparent color, 

 and loses iodine, being converted into peroxide and carbonate. 



5. The starch may be replaced by any other substance having a 

 a tendency to unite with iodine. 



6. A mixture of iodide of lead and starch remains unaltered in 

 diffuse daylight, but becomes of a dark blue color when exposed 

 to the direct rays of the sun. 



Chloride of lead {plvbamed) is not affected in any way by expo- 

 sure to light. , 



ABSORPTION BY THE SKIN. 



In a paper addressed to the French Academy of Sciences, Dr. 

 Scouttetten says the absorbing power of the skin may be promoted 

 or prevented, according to the form under which the substance to 

 be absorbed is applied to it. It is well known that the skin con- 

 tains a large number of follicles, by which fatty matter is secreted, 

 intended to lubricate it, and maintain it in a state of suppleness. 

 The skin also contains glands which secrete perspiration. Perspi- 

 ration, in being evaporated, does not carry away the various salts 

 held in solution, but deposits them on the fatty matter, where they 



