NITROGEN. 17& 



This method may be modified in many ways. The potassium 

 bisulpbate may be omitted, but the digestion then takes longer. 

 Copper oxide or sulphate may be substituted for the mercury ; 

 if this be done, the potassium sulphide solution may be replaced 

 by an equal bulk of Soxhlet's alkaline tartrate solution (see 

 Estimation of Milk-Sugar, p. 160). 



The tube with two bulbs can be replaced by any other form of 

 apparatus having for its object the prevention of splashing ; for 

 the copper flask a Jena or other glass flask, or even a tin bottle, 

 may be used. If a tin flask is employed, it must be remembered 

 that " rust " contains ammonia, and the tin must be boiled with 

 strong soda solution before use ; for this reason a tin flask cannot 

 be recommended. 



For the estimation of nitrogen the methods of Varrentrap and 

 Will and of Dumas may be employed, but they are not so gene- 

 rally convenient. In large laboratories where many deter- 

 minations are made the method of Dumas is perhaps more 

 convenient than that of Kjeldahl ; these methods will be found 

 described in manuals devoted to analytical chemistry. The 

 method of Kjeldahl is, however, the most generally employed in 

 milk analysis. 



Bitthausen's Method is performed as follows : Ten grammes 

 of milk are diluted to about 100 c.c. and 5 c.c. of Soxhlet's copper 

 sulphate solution (see Estimation of Milk-Sugar, p. 160) added ; 

 a solution of caustic soda (25 grammes per litre) is added, drop by 

 drop, till the solution is nearly neutral. The precipitate settles 

 rapidly ; an excess of alkali must be avoided, as it prevents 

 precipitation of the proteins. The precipitate is allowed to settle, 

 and the supernatant liquid poured off through a tared filter, or 

 Gooch crucible. The precipitate is washed several times by 

 decantation, and then transferred to the filter or crucible, the 

 portions adhering to the beaker being removed by a " policeman." 

 It is washed a few more times with water, and the filter or 

 crucible allowed to drain. 



The filter or crucible is washed once with strong alcohol, and 

 then several times with ether, preferably in a Soxhlet extractor ; 

 it is then washed with strong alcohol from a small wash bottle,, 

 using the jet to distribute the precipitate over the filter. 



The filter or crucible and its contents and the tare 

 are dried in an air oven at a temperature of 130 C. 

 and weighed ; the filter or crucible and precipitate are inciner- 

 ated in a porcelain capsule in a muffle, going up to as high a 

 temperature as possible. The weight of the residue, minus that 

 of the ash of the filter, is subtracted from the weight of the 

 dried precipitate, the difference being the proteins. 



The author and Boseley have obtained good results by neutral- 



