76 CHEMICAL EXAMINATION 



proteids. It is also pointed out that as caseinogen and albumin 

 do not give the same aldehyde value, the factor is only applica- 

 ble when the ratio of caseinogen to albumin is normal. 



Mineral Constituents. The estimation of the mineral 

 constituents in milk is but infrequently required in connection 

 with public health work but on these occasions, the following 

 method, due to Droop Richmond, will be found advantageous 

 as it secures fairly accurate results with a minimum expenditure 

 of time and labour. 



Fifty grams of milk are evaporated and charred to a black 

 ash : the mass is extracted with hot water and filtered, the insol- 

 uble portion, together with the paper (after washing) being 

 ignited until white; this gives the insoluble ash. Evaporation 

 of the filtrate and cautious heating gives the weight of the sol- 

 uble ash. 



The soluble ash, after solution in water, is made up to a 

 known volume and aliquot portions used for the determination 



N 

 of the alkalinity by titration with acid with methyl orange 



N 

 as indicator, and chlorine by titration with silver nitrate, 



N 

 using potassium chromate as indicator. 1 c.cm. of acid 



= 0.0031 grm. Na 2 and 1 c.cm. ^ AgN0 3 = 0.00355 grm. Cl. 



The insoluble ash is dissolved in a slight excess of dilute 

 hydrochloric acid, and the solution (nearly neutralised if nec- 

 essary) heated to boiling; a cold saturated solution of ammo- 

 nium oxalate is dropped in slowly until further addition pro- 

 duces no further precipitate. After standing at least two hours, 

 the precipitate is filtered off, washed, and ignited at a low tem- 

 perature to convert the oxalate into carbonate; it is advisable 

 to moisten the ignited precipitate with ammonium carbonate 

 solution and reignite at a very low temperature. The precipi- 

 tate, after weighing, is dissolved in dilute hydrochloric acid, 

 keeping the bulk small, ammonia is added to alkaline reaction, 



