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LIV. Observations on the frequent Presence of Lead in En- 
glish Chemical Preparations ; on the Cause of that Pre- 
sence; and other Remarks relative thereto. By Gustavus 
ScHWEITZER*. 
THE examination of the purity of chemical preparations, 
in which I have been engaged for some time, convinces 
me that many of them are impure and contain lead. In se- 
veral which I have examined I have found subcarbonate of 
magnesia containing lead in the proportion of 2°40 grains 
subcarbonate of lead in 1000 grains of subcarbonate of mag- 
nesia. Bicarbonate of potash contained a similar proportion ; 
bicarbonate of soda, subcarbonate of ammonia, &c. showed 
the same impurity. It is clear, when these substances, so 
universally used, contain lead, that many other combinations 
which are prepared from them must be equally impure. The 
cause of this impurity arises greatly from the manner in which 
these substances are prepared. Leaden vessels are too often 
used for the crystallization and precipitation of them, and how 
easily alkaline substances act on lead is too well known to 
need comment. But another cause of this impurity, although 
the portion present is but very small, is the white glass used 
in this country, which must be an object of great consequence 
to practical chemists and druggists. I know not whether any 
direct experiments have been made to show what influence 
alkalies, acids, and salts may have on white glass. I have 
therefore endeavoured to ascertain this point by the following 
experiments. White glass bottles, such as are used for medi- 
cine, were taken and filled, some with distilled water and 
others with common water. No lead was imparted to the 
water in either case, even after immersion in it for a few 
weeks exposed to a common temperature; but when the di- 
stilled water was impregnated with carbonic acid gas, after a 
few days the fluid gave, with the proper tests, ample proof of 
the existence of lead; and when boiled to expel the gas, no 
indication of lead was obtained, proving that a bicarbonate of 
lead was formed by the action of the carbonic acid gas on the 
lass. Acetic acid, nitric acid, muriatic acid also take up 
an from white glass. Diluted sulphuric acid, after standing 
some time in these glasses, shows no indication of dissolved 
lead, but after pouring off the acid and rinsing the bottle 
with nitric acid the presence of lead was detected. Neutral 
salts showed an equal action when they contained such acids 
as produce with oxide of lead insoluble combinations, or com- 
* Communicated by the Author. 
2E2 
