THE TECHNOLOGIST. [March 1, 1865. 



350 ON CHEMISTRY APPLIED TO THE ARTS. 



chloride of gold, and 1 part of caustic potash. Each of these should 

 be added successively, and the whole of the liquor carried to the boil 

 and filtered. It is then ready for gilding silver or brass objects, when 

 properly attached to the pole of a galvanic battery. The silvering 

 liquor is made by substituting for the chloride of gold, in the above 

 process, ferrocyanide of silver, prepared by adding nitrate of silver to a 

 solution of ferrocyanide of potassium, the white precipitate resulting 

 being washed and added to the liquor intended for silvering. For 

 covering zinc or iron with copper it is simply necessary to substitute the 

 ferrocyanide of copper for that of silver. Ferrocyanide of potassium, 

 as above stated, is also employed for the manufacture of Prussian blue, 

 which was accidentally discovered by Diesback, in 1718, by adding 

 alum, containing iron, to the ammoniacal liquors sold to him by 

 Dippel, which were produced, a3 already stated, during the distillation 

 of animal refuse. These liquors, being rich in cyanide compounds, 

 yielded, with the salt of iron of the alum, Prussian blue. At the pre- 

 sent day Prussian blue is manufactured by different processes, but they 

 are all based on the principle of mixing various salts of iron with red 

 or yellow prussiate, when double cyanides of iron (or Prussian blues) 

 are produced. 



I shall now examine with you some of the various causes which 

 contribute to the destruction of animal matters, when it arises from 

 slow decay or putrefaction. The first of these to which I shall have the 

 pleasure of calling your attention is that observed by Dr. Stenhouse, 

 who, in 1854, made the curious discovery, that if the body of an animal 

 be buried in a carbonaceous mass, such as charcoal, after a few months 

 the whole of the animal, excepting the skeleton, would entirely disap- 

 pear : and what was still more remarkable was, that, though the ex- 

 periments were conducted within his laboratory, no unpleasant effluvium 

 was apparent to those who were constantly there. This eminent 

 chemist attributed the rapid and complete destruction of animal tissue 

 in these experiments to the oxidation of the animal matters by the oxy- 

 gen of the atmosphere ; but to enable you fully to understand how this 

 occurs, I must call your attention to the following facts. Lowitz, many 

 years since, observed that charcoal possesses the property of absorbing 

 and condensing in its pores large quantities of various gases, and 

 Theodore de Saussure made an extensive series of experiments, from 

 which I extract the following data : — 



One cubic inch of boxwood charcoal absorbed of — 



Ammonia 90 cubic inches. 



Hydrochloric acid .... 85 „ „ 



Sulphurous acid .... 65 „ „ 



Sulphuretted hydrogen 55 „ „ 



Carbonic acid 35 „ „ 



Oxygen 10 „ „ 



Nitrogen 7 „ 



