Chemical Notices : — M. Stahlschmidt on Nitride of Iron. 249 



350, and in a gas-flame about 1000 times as great as that which 

 appears in the luminous rays. 



Reduced to mechanical measure, the mechanical equivalent of 

 light is as follows : 



The unit of the quantity of work in a second, that is, 1 kit. raised 

 to a height of 1 metre in a second, is equal to that which the lumi- 

 nous rays contain which issue from a source of light whose lumi- 

 nous intensity is 34' 9 times as great as that developed by a candle 

 which burns 8*2 grw.s. of spermaceti in an hour. 



This is the maximum of the mechanical equivalent of light ; 

 it may possibly still be somewhat reduced by subsequent expe- 

 riments, but the equivalent is in any case very small. I shall 

 subsequently continue the investigation with more intense light, 

 as solar and the electric light. 



XXXIV. Chemical Notices from Foreign Journals. 



By E. Atkinson, Ph.D., F.C.S. 



[Continued from vol. xxix. p. 538.] 



FROM numerous investigations on nitride of iron, it would 

 appear that iron is capable of uniting with nitrogen in nume- 

 rous proportions, and thus can alloy itself with a nitride of iron of 

 definite composition. Stahlschmidt* has recently investigated 

 the preparation and properties of nitride of iron, and finds that 

 nitrogen unites with iron in a perfectly definite proportion, and 

 that all the different nitrides of iron, the existence of which has 

 been assumed, must be regarded as mixtures of this definite 

 nitride with pure iron. 



The mode of preparation he adopted was that of Regnault and 

 TYemy, which consists in passing ammonia over pure protochlo- 

 ride of iron. The temperature at which the action takes place 

 may be very low — far under the red heat ; and that chloride 

 which is exposed in a thin layer passes almost immediately into 

 nitride, while thicker masses require a longer time. Nitride of 

 iron prepared at different temperatures contains different pro- 

 portions of nitrogen ; and the proportion is in general smaller 

 the lower the temperature. The best results are obtained when 

 the chloride is exposed in a very thin layer to the action of am- 

 moniacal gas at a temperature at which the chloride of ammonium 

 formed is just volatilized. The nitride of iron obtained thus, 

 partly in thin laminae and partly as a grey powder, has exactly 

 the composition N Fe 4 , and is thus an ammonium in which all 

 hydrogen is replaced by iron. It contains 11*1 per cent, of 

 nitrogen. 



* Poggendorff's Annalen, May 18G5. 



