One-half cubic centimeter (10 drops) of alumina cream (prepared as 

 described in Bulletin No. 46 J ), and 1.5 cubic centimeter of lead sub- 

 acetate are then added and the contents well shaken. The mixture is 

 allowed to stand from forty-five to sixty minutes, occasionally giving 

 the tube a twisting motion to facilitate the settling of the precipitate. 



The tube with its holder is then placed in the centrifugal machine 

 and run six minutes (see conditions given below). At the end of six 

 minutes the contents of the tube are examined, and if any material 

 adheres to the side of the wider portion it is loosened by means of a 

 small wire provided with a loop at the end. The tube is returned to the 

 centrifuge and run six minutes longer at the same rate. The volume 

 of the precipitate is noted, estimating 0.01 cubic centimeter as closely 

 as possible. A blank, using water 2 and the reagents named above, is 

 run as often as necessary in order to be certain of its value. The blank 

 reading is subtracted from the reading given by the precipitate in each 

 case. In the case of a sirup the result is reduced to the 5-gram basis 

 by dividing by the specific gravity of the sample. If the sugar content 

 of the sample is known, the specific gravity may be found from tables. 3 

 Usually 1.330 has been found very nearly correct for maple sirup. 



DISCUSSION. 



The centrifugal machine used in this laboratory has a radius of 18.5 

 cm, and a speed of 1,600 revolutions per minute has been adopted. 

 Calling M unity in the formula 



F = , then F = Y , and v - ^Fr. 



From the above a numerical expression for F can be computed, and 

 having measured r for a given machine, the value of v and the required 

 number of revolutions per minute can be found. 



The results obtained by the author 4 show why a total run of twelve 

 minutes was adopted. Such results can possibly be made to agree more 

 closely under more perfect conditions. The results were obtained on 

 5-cc samples and have not been reduced to results on the 5-gram basis. 

 The mean blank at the end of twelve minutes was 0.44 cc. 



The precipitates vary in the pure sirups from 0.94 to 1.82 cc, and in 

 the pure sugars from 1.18 to 4.41 cc. The highest results, especially 

 among the sugars, are apt to occur in samples which have not been 

 properly clarified. In well clarified samples the precipitates will be 

 found, as a rule, between 1.00 and 1.20 cc for sirups, and between 1.20 



1 U. S. Dept. Agr., Bureau of Chemistry, Bui. 46, Methods of Analysis, p. 39. 



2 Cane-sugar solution of sp. gr. 1.330 is suggested ; the blank would be a trifle 

 higher. 



"IT. S. Dept. Agr., Bureau of Chemistry, Bui. 65, Table VI, p. 139. 

 4 Am. Chem. Soc., 1904, 26: No. 11, p. 1523. 



