CHEMICAL SCIENCE. 251 



this adulteration would be likely to produce in the employment of 

 such lards for some pharmaceutical purposes, and the danger which 

 might ensue from its application to machinery. In another communi- 

 cation from Mr. Calvert, of Manchester, that gentleman confirms Mr. 

 Whipple's statement, and informs us, in addition, that the American 

 lard analyzed by him contained from 10 to 12 per cent, of water, 2 to 

 3 per cent, of alum, and about 1 per cent, of quicklime. The quan- 

 tity of alum, it is supposed, is added by the manufacturer for the pur- 

 pose of communicating to the lard the property of facilitating the 

 rising, and increasing the whiteness of the confectioner's paste, in 

 which it is largely employed. 



METHOD OF RESTORING OIL PAINTINGS. 



One of the chief drawbacks to the employment of white-lead in 

 artistic painting, consists in the facility with which it becomes black- 

 ened by the sulphuretted hydrogen, and hydrosulphuret of ammonia, 

 both so prevalent in the atmosphere of towns. A very elegant way 

 of instantaneously by restoring those discolored parts to their original 

 whiteness was suggested by M. Thenard, the discoverer of peroxide 

 of hydrogen, otherwise called oxygenated water. It is a prominent 

 quality of this liquid to impart oxygen and hence if applied to a 

 coating of black sulphuret of lead, the latter immediately acquires 

 oxygen, and is changed into the white sulphate, thus restoring the 

 original tint. Unfortunately, however, this peroxide of hydrogen is so 

 difficult of manufacture, and so expensive, that its use for the purpose 

 in question is almost impossible. A much easier plan, but founded on 

 the same principle, has been suggested by M. Schonbein, of Bale, who 

 in the course of his studies on ozone, discovered that oil of turpentine 

 if exposed in an open glass vessel to the atmosphere in the sun's rays, 

 and agitated from time to time during the space of two or three 

 months, acquired such oxydising properties, that it was capable of 

 acting on sulphuret of lead just like the oxygenated water of Then- 

 ard, that is to say, capable of changing it almost instantaneously into 

 the white sulphate. Professor Schonbein has himself suggested the 

 value of this oxygenized oil of turpentine to artists and picture-dealers. 

 Many other liquids, besides oil of turpentine, can be oxygenated in a 

 similar manner, and would probably be as advantageous. 



LIQUID INDIA RUBBER. 



A new method of preparing the gum of the india-rubber tree, has 

 recently been brought out. The milk as drawn from the tree, is 

 bottled in large glass bottles, or demijohns. A preparation of some 

 chemical nature, (understood to be a salt of ammonia,) is mixed with 

 the milk, and the bottles are securely sealed. In this way the gum is 

 exported. It curdles twenty-four hours after exposure to the air, and 

 forms a pure, white, solid, and remarkably strong rubber. 





