24: INTRODUCTION. 



in which V represents the volume of gas, t its tem- 

 perature, B the pressure under which the gas stands 

 (height of barometer), expressed in millimetres, /the 

 tension of water vapor at the temperature , and 

 0.001256 the weight of 1 cc. of nitrogen at 0, and 

 760 mm. pressure. 



When an organic compound contains chlorine, bro- 

 mine, iodine, or sulphur, it must in most cases be tho- 

 roughly decomposed, before these can be detected by 

 ordinary reagents and estimated. The estimation of 

 the halogens is accomplished by igniting the substance 

 with pure lime, free from water ; the estimation of sul- 

 phur by heating with nitric acid in sealed tubes, or 

 igniting with a mixture of sodium carbonate and po- 

 tassium nitrate. Chlorine, bromine, and iodine can in 

 many cases be detected in the ordinary manner, and 

 estimated by previously treating the substance with 

 hydrogen in statu nascendi (from sodium-amalgam and 

 water). 



As an example of the method of calculating an ele- 

 mentary analysis, that of acetic acid may be taken. 



0.234 grm. of acetic acid were ignited with copper 

 oxide. The gain in weight of the calcium chloride 

 tube amounted to 0.1405 grin.; that of the potassa 

 bulbs and tube 0.3432 grm. From 0.234 grm. acetic 

 acid were hence produced 0.1405 grm. of water, and 

 0.3432 grm. carbonic acid, and these contain 0.0156 

 grm. hydrogen, and 0.0936 grm. carbon. These num- 

 bers show 4^0.00 per cent, of carbon, and 6.67 per cent. 

 of hydrogen. As acetic acid only contains carbon, 

 hydrogen, and oxygen, its composition expressed in 

 percentages is 



C = 40.00 per cent. 

 H= 6.67 " 

 = 53.33 



In order to find the atomic proportion from these 

 numbers, we must divide them by the respective 

 atomic weights of the elements. 



= 40.00-12 = 3.33 



H= 6.67- 1 = 6.67 



= 53.33 - 16 = 3.33 



