422 On Nitrogen Deteiininations. 



between this cloud, aud the extremity of the slender tube whence 

 the gas was disengaged, might be increased to 10 millims. 



13. It is evident that iu the experiment of M. Bosscha, the 

 production of the sound must be attributed to the cooling and 

 consequent contraction of the heated gas, by the wire-gauze 

 disc through which it passes. This experiment may be con- 

 sidered the inverse of those that precede. 



Leyden, 27th April, 1859. 



LXXII. Chemical Notices from Foreign Journals. By E. Atkin- 

 son, Ph.D., F.C.S., Teacher of Physical Science in the Chel- 

 tenham College. 



[Continued from p. 280.] 



LIMPRICHT* made the observation that carbonic acid 

 passed over metallic copper at a dull red heat, was par- 

 tially reduced to carbonic oxide, and that hence the usual me- 

 thods of analysing nitrogenous substances in which the use of 

 metallic copper was involved, wei'e liable to error. This obser- 

 vation led to some experiments by Lautemannt, who confirms 

 the statement as far as concerns the use of the porous spongy 

 copper obtained by reducing granulated oxide of copper. In 

 one case he found that when carbonic acid was passed over a 

 layer of granulated oxide of copper 30 centims. long, about li 

 per cent, was reduced to carbonic oxide. But the use of freshly- 

 reduced copper turnings is not liable to this error. In a special 

 case, with a layer the same in length as in the previous case, the 

 amount of carbonic oxide formed was only 0'05 per cent, of the 

 carbonic acid passed over — an amount which may safely be 

 neglected. The error may also be obviated by placing a layer 

 of oxide of copper in front of the metallic copper. 



In connexion with this subject, Perrot J found that pure cop- 

 per turnings do not decompose carbonic acid ; but if the copper 

 be not quite pure, and contains iron or zinc, part of the car- 

 bonic acid is reduced with formation of carbonic oxide. 



In a connnunication on chlorous acid, Schiel§ states that by 

 observing a few precautions its preparation may be effected with- 

 out danger, and almost as conveniently as that of chlorine. The 

 method he uses is that of Millon ; and the proportions are 2 parts 

 chlorate of potash, 3 parts nitric acid of 1*30 sp. gr., 0'6 to 0*8 

 parts cane-sugar, and 8 to 4 parts of water. It is necessary that 

 the chlorate of potash and the nitric acid be pure, although the 



* Lii'big's AnnaUn. October 18.58. t Ibid. March 1859. 



X Ibid. March 1859. § Ibid. February 1858, and March 1851). 



