ON GLYCERIN. 
evaporated to the consistence of a thin syrup, and treated 
with sulphuretted hydrogen, until a precipitate ceases to 
be thrown down; when it is filtered, boiled, and evaporated 
by a gentle heat, until it ceases to lose weight. It is gene- 
rally colored as thus made, and requires to be passed through 
animal charcoal. 
There is some difficulty in obtaining glycerin colorless, 
unless the water is driven off, before decolorization is at- 
tempted ; as in evaporation even by a water bath, considera- 
ble color is obtained. The thickness of the liquid, renders 
its passage through the animal charcoal slow, but if thus 
prepared, a beautiful article can be obtained, very much 
the color and consistence of good castor oil. That sold as 
glycerin is considerably diluted, seldom having a greater 
specific gravity than 1.15 to 1.18, while the pure is 1.25 to 
1.27. 
With regard to the yield as thus prepared, an approxima- 
tion was attempted by the following experiment. Three 
gallons of olive oil, and 15 lbs. (Troy) of English litharge, 
were made into a plaster, and three gallons of hot water 
added, and thoroughly mixed. The whole was then allow- 
ed to cool, and the liquid accurately drawn off. This was 
evaporated to the spec. grav. of 1.15, treated with sulphur- 
etted hydrogen, filtered, boiled, and further evaporated, 
until 18 oz. (av.) Glycerin were obtained, of the specific 
gravity 1.25. There is an advantage in not allowing the 
liquid to become so concentrated, before sulphuretted hy- 
drogen is passed into it, as, when it is too thick, its further 
treatment is rendered more difficult, both to filter the solu- 
tion clear, and to get rid of the excess of gas, which under 
all circumstances it is not easy entirely to remove. About 
1.1 is a proper density for its addition. 
To ascertain the actual quantity of glycerin existing in 
olive oil, or rather separable by the usual method, half a pint 
of the best olive oil, was made up with 31 ounces (Troy) En- 
glish litharge, into lead plaster. This was thoroughly de- 
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