108 FOODS AND FOOD ADULTERANTS. 



fact, iiot well recognized, combined with the knowledge that in the proc- 

 ess of evaporation many particles of sugar must be occluded by the 

 hardening caseine, tends to throw doubt upon the accuracy of estimat- 

 ing the sugar by the extraction method. 



The work which I undertook had for its object the determination of 

 the best method of preparing the milk-sugar solution for the polari- 

 scope, and a comparison of the numbers obtained by this instrument 

 with those given by the ordinary process of extraction. 



The reagents used for removing the albumens were : 



(1) Saturated solution basic lead acetate, specific gravity 1.97. 



(2) Nitric acid solution of mercuric nitrate diluted with an equal vol- 

 ume of water. 



(3) Acetic acid, specific gravity 1.040, containing 29 per cent. H0 2 Er 3 

 O 2 . 



(4) Nitric acid, specific gravity 1.197, containing 30 per cent. HNO 3 . 



(5) Sulphuric acid, specific gravity 1.255, containing 31 per cent. H 2 S 

 4 . 



(6) Saturated solution sodium chloride. 



(7) Saturated solution magnesium sulphate. 



(8) Solution of mercuric iodide in acetic acid; formula 1 KI, 33.2 

 grams Hg 01 2 , 13.5 grams. Strong HO 2 H 3 O 2 , 20.0cc. Water, 64.0cc. 



Alcohol, ether, and many solutions of mineral salts, hydrochloric, and 

 other acids were also tried as precipitants for albumen, but none of 

 them presented any advantages which would make a detailed account 

 of the experiments of any interest. 



Table No. 9 contains a record of the experiments which led to the adop- 

 tion of Ice. acetate of lead solution, or Ice. acid mercuric nitrate, as the 

 best amount of each for 50cc. of milk. 



Nearly all the polarisations were made in a 400mm. tube. From two to 

 four observations were made with each sample. An average of these 

 readings was taken for each determination. In the calculations the 

 value of (a) D was taken at 53 instead of 52.5, the number which subse. 

 quent investigations have led me to believe more exact. The instru- 

 ment employed was a u Laurent Large Model" polariscope. 



In all cases the volume of the solution was corrected for the volume 

 of the precipitated caseine. The volume was assumed to occupy 2cc. for 

 each 50ce. milk. 



Since in the Laurent instrument the weight of sucrose in lOOcc. to read 

 even degrees on the scale is 16.19 grams f(a) D =66.67], it follows that 

 the weight of lactose in lOOcc. to read one degree on the scale for each 

 percent, lactose present would be 1G.19 : #=53: 66.67; #=20.37." 



If 52.5 be taken as the value of (a) v for lactose, then # = 20.56. 



In table No. 9, A indicates acetic acid, Pb basic acetate of lead, MR 

 acid mercuric nitrate, &c. The letters O and H indicate the tempera- 

 ture ; C denoting the ordinary temperature of the room, and H that the 

 sample was heated to 100 C. and cooled before filtering. 



1 Jour, de Pharm. ot do Chini., vol. 10, p. 108. 



