108 ESTIMATION OF TOTAL SOLIDS AND ASH. 



alkaline with ammonia. The precipitate is washed well, and 

 the filtrate evaporated and ignited very cautiously ; the weight 

 will give the alkaline chlorides. The residue is dissolved in 

 water, and the solution should be quite clear ; if it is not so, 

 a little ammonium carbonate is added, the liquid evaporated to 

 dryness, and the residue ignited cautiously ; the residue is again 

 taken up with water, the solution filtered and evaporated, and 

 the residue ignited cautiously and weighed. 



The chlorine in this may be titrated by standard silver nitrate, 

 using potassium chromate as indicator. The potassium and 

 sodium are calculated by the following formula : 



Let W = weight of alkaline chlorides 

 and C = weight of chlorine therein. 



The weight of sodium = 2-997 C 1-4254 W. 

 potassium = 2-4254 W 3-997 C. 



The potassium may be estimated directly by evaporating the 

 solution of alkaline chlorides with an excess of platinum tetra- 

 chloride solution almost to dryness ; the pasty residue is treated 

 with 80 per cent, alcohol containing about 5 per cent, of ether, 

 and washed repeatedly with this ; the alcohol is passed through 

 a weighed filter or, preferably, a Gooch crucible, and the preci- 

 pitate is finally transferred to this and washed with ether. It is 

 then dried at 100 C. and weighed ; the weight multiplied by 

 0-3056 will give the potassium chloride ; this subtracted from 

 the weight of the alkaline chlorides will give the sodium chloride. 



The potassium chloride multiplied by 0-5244 will give potassium 

 and by 0-6314 potash. The sodium chloride multiplied by 0-3932 

 will give sodium and by 0-5299 soda. 



The above scheme of analysis has been worked out so as to 

 use as little milk as possible, as the amount available is some- 

 times limited. Many obvious modifications are available and 

 will readily suggest themselves to analysts ; thus the chlorine 

 may be estimated gravimetrically, or the perchlorate method 

 used for potassium, and, if the amount of milk be sufficient, the 

 phosphoric acid may be separated from another portion by the 

 molybdic acid method. Such modifications will be found in 

 works on inorganic analysis, and need not be described. 



If boric acid be present, it will be found to interfere with 

 the results of the analysis, as a portion of this remains in the 

 insoluble ash; this may be removed by evaporating the acid 

 solution to dryness and evaporating repeatedly with small por- 

 tions of methyl alcohol. It will also interfere with the estimation 

 of alkalinity in the soluble ash, as the alkali shown by methyl 

 orange will be due to borax ; the chlorine is best estimated in 

 this case gravimetrically as silver chloride. 



