127 



method, however, is only applicable when the amount of carbon con- 

 tained in the substance is known, and would not apply to those ana- 

 lysis in which the nitrogen alone required to be determined. Hav- 

 ing, as in the previously described operation, collected the mixed 

 gases in graduated tubes, their united volume is read off and noted. 

 After thil has been done, caustic potash ley is introduced to absorb 

 the carbonic acid. The residual gas, which is nitrogen, is then mea- 

 sured, and the proportion between the volumes of the two gases is at 

 once Iscertained. Now, as each atom of carbon produces one of 

 carbonic acid, occupying the same space as an atom of nitrogen, the 

 proportion between the number of atoms and the volumes of the 

 two gases will be the same ; and as the number of atoms of carbon 

 is known, that of the nitrogen can be very easily calculated. The 

 principal advantage of Baron Liebeg's method consists in this, that 

 it is not requisite to make corrections for temperature, pressure, or 

 watery vapour contained in the gases, as they are both subjected to 

 the same influences in these respects. 



Either of these methods will, in careful and experienced hands, 

 yield very accurate results ; but the time required, as well as the 

 necessity of using a somewhat complicated apparatus, renders their 

 application to common analyses almost impracticable. 



A much more easily and quickly performed mode of operatmg 

 was proposed a few years ago by Varrentrapp and Will. These 

 chemists ascertained, by a series of very carefully-conducted expe- 

 riments, that all organic bodies containing nitrogen, unless m the 

 form of nitric acid, when heated in contact with a mixture of the 

 hydrates of lime and soda, give off that nitrogen in the form of 

 ammonia; and this being collected in a solution of hydrochloric 

 acid, is converted into the double chloride of platinum and ammonium 

 by the addition of bichloride of platinum ; and this latter substance 

 being carefully washed, dried, and weighed, gives, by a simple calcu- 

 lation, the amount of nitrogen in the analysed substance. 



The method of Varrentrapp and Will, just mentioned, has the 

 great advantage of being much moi-e easily performed than either of 

 the two previously referred to, and at the same time a much less 

 complex form of apparatus may be used in the operation ; neverthe- 

 less, from the necessity ef performing several operations before 

 finally weighing the ammonio-chloride of platinum, several hours 

 must always elapse before the result can be obtained. 



