310 BUTTER. 



3. Four to five grammes of butter are weighed into a wide- 

 mouthed flat-bottomed conical flask, wbich is placed in a water 

 oven and shaken every ten minutes for the first half hour, after 

 which it is shaken every half hour. At the expiration of four 

 hours it is cooled, weighed, and returned to the bath for another 

 hour ; if there be any loss, the drying is continued till an hour's 

 drying does not cause any diminution of weight. 



4. From 2 to 2| grammes of well-mixed butter are weighed 

 into a fiat-bottomed basin about 2| inches diameter. This is 

 placed in the water-oven till just melted, and 1 to li c.c. of 

 strong alcohol are added ; the basin is replaced in the water- 

 oven, and weighed after two hours. The loss represents water. 



Of the four methods, the first is the most expeditious, and is 

 nearly as accurate as the others ; the second is the most accurate ; 

 the third is the most convenient if solids not fat and salt are 

 also estimated ; while the fourth is fairly accurate, rapid, and 

 requires no attention. No one of the four methods has, how- 

 ever, any great advantage over the others. 



Solids not Fat and Salt. — For the estimation of solids not 

 fat and salt the residue from the determination of water is taken 

 and melted at a low temperature. A solvent for the fat, of 

 which ether is perhaps the best, though chloroform, amyl alcohol, 

 and others may be also used, is poured on, the whole well mixed, 

 and allowed to stand in a warm place till the solvent is quite 

 clear. The solution is carefully decanted and a fresh portion 

 of the solvent poured on the residue, and, when clear, poured 

 off. Four or five successive treatments are sufficient to remove 

 the whole of the fat. With a little practice the operation may 

 be so performed that none of the solids not fat are poured away 

 with the solvent. The residue is placed in the water-oven, 

 and dried to constant weight ; the weight represents solids not 

 fat and salt. 



Salt. — To estimate the salt the residue is treated with hot 

 water and filtered, the filter together with the residue washed, 

 and the filtrate, or an aliquot portion of it, is titrated with a 

 standard silver nitrate solution, using potassium chromate as 

 indicator. It is essential that the solution should be cold before 

 titration, and the silver nitrate solution should be standardised 

 on pure sodium chloride. The strength should not be deduced 

 from the amount of silver nitrate present, as Hazen, and, later, 

 W. G. Young, have pointed out that the amount of silver used 

 is always greater than that theoretically required to combine 

 with the chlorine. From the amount of silver nitrate solution 

 used the weight of salt is readily calculated. It is convenient to 

 make the silver nitrate solution of such strength that 1 c.c. 

 = 0"005 gramme of sodium chloride. 



