4? BULLETIN OF THE BUSSEY INSTITUTION. . 
tions unless special precautions be taken. It appears from my 
own experience that, while no precipitate is produced when 
ordinary normal lead acetate is added either to solutions of 
sucrose or dextrose, both these sugars, as ordinarily prepared, 
may yield precipitates with basic lead acetate. In repeated trials, 
slight precipitates fell when a drop of the basic lead acetate * 
was added to solutions of so-called chemically pure sucrose, dex- 
trose or maltose; and although these precipitates were of different 
appearance from the mannose-lead precipitate, they were still 
sufficiently like it to prevent the application of the test when any 
approximation to delicacy was required. These alien precipitates, 
though of similar color (white) to the mannose-lead precipitate, 
do not exhibit the gelatinous appearance of the latter. They are 
much more pulverulent and soon settle to the bottom of the test- 
tube. It was easily shown, by the method of fractional precipita- 
tion, that these pulverulent precipitates were caused by impurities 
in the sugar. On adding a solution of the basic lead acetate, a 
drop at a time and at intervals, to a solution of- sucrose or of 
dextrose and filtering off the precipitates produced by each drop, 
it was seen that precipitation soon ceased and that the formation 
of the precipitates had nothing to do with the actual sugar. 
Usually only a slight milkiness was produced even by the.second 
drop of basic lead acetate added to the filtrate from the precipitate 
caused by the first drop. By proceeding in this way with man- 
nose solutions that were known to contain traces of calcium 
* Several different preparations of basic lead acetate were used in these 
experiments, and it is noteworthy that while all of them did good service, 
some did better than others. Two samples, prepared by heating during five 
or ten minutes an excess of litharge in a solution of normal lead acetate,* 
gave good results. Perhaps the method of heating for ten minutes may be 
better than heating for half an hour as recommended by the books. For most 
of my trials the reagent was prepared after Parrish ¢ by boiling together for 
half an hour, in a flask with a reflux condenser, a mixture of 6.2 grm. of 
normal lead acetate, 3.6 grm. litharge, and 24 cc. of water. The product 
was filtered and kept in well-stoppered bottles. A sample of basic lead 
acetate, prepared according to Wiley,{ did not give so good a precipitate 
with mannose as did the Parrish preparation or those prepared roughly as 
above described. 
* Compare W. T. Brande’s Chemistry, Philadelphia, 1863, page 598. 
} E. Parrish, Introduction to Practical Pharmacy, Philadelphia, 1859, page 538. 
} H. W. Wiley, Principles and Practice of Agricultural Analysis, Easton, Pa., 3. 101. 
