BOYER'5 MODIFICATION OF RUFFLE'S METHOD 345 



crystallization. 94 The best method to dry the salt without de- 

 priving it of its crystal water is to press it between blotting papers. 



As is seen from the above description the method is essen- 

 tially a reduction process by the action of a powerful deoxidizer 

 in the presence of an alkali. The crystals of the thiosulfate salt 

 cannot be brought into direct contact with a pure alkali, like soda 

 or potash, without forming at once a wet mass which would tend 

 to cake and obstruct the tube. The soda-lime is, therefore, a me- 

 chanical device to prevent this fusion. Where many analyses 

 are to be made, an iron tube, for economical reasons, may be sub- 

 stituted for the glass ; but the glass tube permits a more intelli- 

 gent observation of the progress of the analysis. 



Since charcoal has very high absorbent powers it will be found 

 always to contain a little nitrogen which may be in a form to 

 generate ammonia during the combustion. The charcoal used 

 should, therefore, be previously boiled with caustic soda or potash 

 solution, dried, powdered, and preserved in well-stoppered .bot- 

 tles. Although pure sugar is practically free of nitrogen, even 

 when it is used, it is advisable to occasionally make a blank deter- 

 mination and thus ascertain the correction to be made for possi- 

 ble contamination. 



307. Boyer's Modification of Ruffle's Method. The prin- 

 ciple of the method rests on the observation that if nitrates be 

 heated in a combustion tube with calcium oxalate and soda-lime, 

 not more than two-thirds of the total nitrogen appear as ammo- 

 nia ; but if a certain proportion of sulfur be added the whole of 

 the nitrogen is recovered. 95 The process may be divided into 

 two steps ; viz. : 



(1) Action of the calcium oxalate upon the sodium nitrate in 

 presence of soda-lime. 



(2) The action of sulfurous acid and of calcium oxalate upon 

 the sodium nitrate in presence of soda-lime. 



The analysis is conducted as follows : Dry and pulverize one- 

 half gram of nitrate and mix it intimately with 50 grams of the 

 reducing compound containing approximately 10 per cent, sulfur, 



M Journal of the Society of Chemical Industry, 1883, 2 : 21. 



95 Comptes rendus, 1891, 113 : 503. 



