CHTMISTRT. 227 



be present in a body, the spectroscope shows it when it is volatil- 

 ized, or burned. 



SUMMARY OF CHEMICAL NOVELTIES. 



Carbonization of Wood. — ^I. Gillot, in a memoir to the French 

 Academy of Sciences on this subject, says the only condition es- 

 sential for the production of good charcoal is, that the operation 

 shall proceed slowly. The decomposition of wood commences at 

 about the boiling-point of water. During the decomposition, the 

 production of carbonic acid causes a development of heat in the 

 ret(n*t greater than that out of it, when the heat applied approaches 

 300° C. Too rapid an increase of internal heat gives rise to the 

 formation of tar and gaseous products, diminishing in a corre- 

 sponding degree the useful accessory products, as well as the yield 

 of charcoal. The condensed products contain the largest propor- 

 tion of acetic acid (about 28 per cent.) when the temperature of 

 the oven is 218° C. In this way a given amount of wood will 

 yield about two-thirds in weight of charcoal, and 7 or 8 per cent, 

 of acetic acid. 



Electric Gas Signal. — A Berlin mechanic has invented an inge- 

 nious apparatus for giving an alarm in case of the presence of 

 carbonic oxide or coal gas in a room. It consists of a galvanic 

 battery with a bell and a glass tube filled with liquid chloride of 

 palladium. This metallic salt is extremely sensitive to the pres- 

 sure of carbonic-oxide gas. A small quantity of the gas will at 

 once throw down some of the metal from the solution, and this 

 precipitate collecting in the bottom of the tube establishes a con- 

 nection in the current of electricity, and the violent ringing of a 

 bell will warn the sleeper of his danger. 



Bronzing Cast Iron. — The following is a method of giving cast 

 iron the appearance of bronze without coating it with any metal 

 or alloy : "The article to be so treated is first cleaned with great 

 care, and then coated with a uniform film of some vegetable oil ; 

 this done, it is exposed in a furnace to the action of a high tem- 

 perature, which, however, must not be strong enough to carbonize 

 the oil. In this way the cast iron absorbs oxygen at the moment 

 the oil is decomposed, and there is formed at the surface a thin 

 coat of brown oxide, which adheres very strongly to the metal, 

 and will admit of a high polish, giving it quite the appearance of 

 the finest bronze." — American Artisan. 



- Process for Covering Iron and Steel icith Copper without a Battery. — 

 This pro(^ess, due to Herr Graeger, is described in a recent num- 

 ber of the " Polytechnisches Notizblatt." The objects are first 

 vv'ell cleaned, and then painted over with a solution of protochloride 

 of tin, and immediately afterward with an ammoniacal solution 

 of sulphate of copper. The layer of copper thus produced ad- 

 heres so firmly to the iron or steel, that the different objects can 

 be rubbed and polished with fine chalk without injuring the de- 

 posit. The tin solution is prepared with 1 part of crystallized 

 chloride of tin, 2 parts of water, and 2 parts of hydrochloric acid ; 



