670 APPENDIX. 



It is founded upon the great affinity which exists between 

 azote and hydrogen. Whenever any substance containing azote 

 and hydrogen is heated in contact with potash, lime, barytes, &c. 

 it always gives out ammonia. Now ammonia is a compound of 

 Az H 3 . Almost every organic body containing azote contains 

 also hydrogen ; and the quantity of hydrogen is always sufficient 

 for converting the azote into ammonia. This conversion al- 

 ways takes place. Hence we may determine the quantity of 

 azote in any substance, by ascertaining the weight of ammonia, 

 which it gives out when decomposed. Such is the basis of the 

 method of Varrentrapp and Will. 



Guy-Lussac has shown, that, if hydrate of potash be mixed 

 with an organic body destitute of azote, the water of the hydrate 

 is decomposed ; its oxygen uniting with the carbon and hydro- 

 gen of the organic body, while its hydrogen is disengaged in the 

 state of gas. The products formed by this energetic process of 

 oxydizement vary according to the temperature to v/hich the mix- 

 ture is exposed, and according to the constitution of the organic 

 body. It is enough to state here, that when the organic body is 

 destitute of azote, hydrogen gas is disengaged. When the or- 

 ganic body contains azote, this free hydrogen unites with the 

 whole of that azote, and is converted into ammonia. This pro- 

 cess has been long in use to ascertain whether an organic body 

 contains azote or not 



When a substance contains a great deal of azote, as uric acid, 

 melamin, mellon, &c., it is natural to suppose that the whole 

 azote may not be converted into ammonia, A portion of it may 

 unite with part of the carbon of the substance, and form cyano- 

 gen, and this cyanogen (as also cyanic acid) may unite with the 

 alkali or its bases. And as such a combination may resist de- 

 composition at a high temperature, we may conjecture that a por- 

 tion of the azote may be retained, and not make its appearance 

 in the state of ammonia. 



But Drs Varentrapp and Will have ascertained by direct ex- 

 periment that when a sufficient quantity of hydrate of potash is 

 employed, and when the heat is not too low, the whole azote, even 

 in the compounds just mentioned, is converted into ammonia. 

 When cyanodide of potassium, cyanate of potash, or paracyanic 

 acid is heated to redness with an excess of hydrate of potash, or 

 with a mixture of hydrate of potash or soda, with caustic lime, an 

 abundant evolution of ammonia takes place, and in the residue, 



