216 Notices of the Labours of Contijiental Chemists. 



not yet sufficiently considered, and as I have already tres- 

 passed much on your valuable space, I shall reserve it for a 

 future communication. 



/I 2 



It also remains to obtain the more general value of — 3- men- 



tioned at the commencement of this paper, on the supposition 

 that the particles of the transparent body are composed of 

 atoms of different kinds. 



I intend also to proceed to a second approximation in the 

 solution of the equations (1.) and (2.), on the supposition that 

 a-i^iyi are 7ioi the same for all particles under the sign 2; 

 which I feel pretty sure will lead to the following result, viz. 

 that the velocity of propagation of plane waves depends in 

 some small degree on their position with respect to the axes 

 of symmetry. As we know experimentally that this is not 

 the case, we may hence conclude, that our Hrst approximation 

 was sufficiently near the truth. I believe also that the result 

 of this second approximation may be made use of to prove 

 that the hypothesis of finite intervals cannot be correct. 



Brighton, Dec. 2/, 1841. 



XXXI. Notices of the Results of the Labours of Continental 

 Chemists. By Messrs. W. Francis and H. Choft. 



[Continued from p. 39.] 



Neli) Method of determining Nitrogen in Orgastic Compounds. 

 By Drs. Varrentrapp and Will. 



^ I "'HE nitrogen in organic substances, when not contained in 

 ■* them in the form of ammonia, is always determined quan- 

 titatively by burning them with the oxide of copper, absorbing 

 by an alkali the carbonic acid formed, and measuring the vo- 

 lume of nitrogen gas set free. Even in the analysis of certain 

 ammoniacal compounds, as the ammoniacal salts of organic 

 acids, it has generally been preierred to determine the amount 

 of ammonia by ascertaining the volume of nitrogen. The prin- 

 cipal objection to be made to the methods generally in use, 

 which, though different in their execution, do not differ in prin- 

 ciple, is, that the amount of nitrogen is not determined by 

 weight, but by measuring the volume of the gas. The doubts 

 still existing as to the constitution of many organic bases and 

 of numerous indifferent niti'ogenous compounds, are not solely 

 owing to a want of knowledge of their true atomic weight, but 

 likewise of the actual quantity of nitrogen they contain. The 

 determinations of the nitrogen in most of the organic substances 

 which contain but a small cjuantity of that element, even when 



