VARIETIES. 
177 
thick filter, and the moisture expressed. The moisture, after evaporation, 
still furnishes some caffein. The impure caffein is freed from oil by pres- 
sure between folds of blotting paper, and purified by solution in water with 
animal charcoal, and is afterwards obtained in shining, white, silky crystals. 
Iu general, not more than three drachms were procured from five pounds 
of coffee, from ten pounds seven drachms, and from one hundred pounds, 
the largest quantity, viz : six ounces and four scruples of caffein ; a proof 
that a large quantity must be operated upon if, in a quantitative respect, a 
satisfactory result is to be obtained. Thus it is seen, that good Brazilian 
coffee contains 0.57 per cent, of caffein. At the same time it may be ob- 
served that it contains about ten per cent, of a green liquid oil, and two per 
cent, of a yellow, firm fat (Palmtin.) — Phar, Journ. andArcMv der Phar- 
macie, November, 1851. 
Filter Accelerator. — M. Dublanc describes an arrangement to accelerate 
the filtering process, which consists of a funnel-shaped tissue of plated or 
tinned wire on which the filter is supported in the funnel. It is shaped 
like a plaited filter, and is made from a flat circular piece of wire gauze, 
crimped in plaits running from centre to circumference so as to give it the 
shape of a funnel with fluted sides. — Journ. de Pharm., February, 1852. 
A New Test for Mercury. — If a strong solution of iodide of potassium be 
added to a minute portion of any of the salts of mercury, placed on a clean 
bright plate of copper, the mercury is immediately deposited in the metallic 
state, appearing as a silvery stain on the copper, which cannot be mistaken, 
as no other metal is deposited by the same means. 
By this method corrosive sublimate may be detected in a drop of solution 
unaffected either by caustic potash or iodide of potassium. In a mixture 
of calomel and sugar in the proportion of one grain to two hundred, a dis- 
tinct metallic stain will be obtained with one grain, which of course contains 
l-200th of a grain of calomel ; in like manner l-400th of a grain of per- 
oxide of mercury maybe detected, although the mixture with sugar is not 
in the least colored by it. 
With the preparations of mercury in the undiluted state, this process 
acts with remarkable accuracy, the smallest possible quantity of calomel 
or peroxide of mercury, such as would almost require a magnifying lens to 
perceive, placed on copper and treated with iodide of potassium, will give 
a distinct metallic stain. 
The advantages of this test may be briefly stated as follows: — 1st, It is a 
delicate test, inferior only to chloride of zinc and the galvanic test of zinc 
and gold. 2d. It is easy of application. 3d. It requires a very small por- 
tion of the substance to be examined — a matter of no small import. 4th. 
Acting on the insoluble as well as the soluble salts, it obviates the interme- 
diate process of solution. 5th. When it acts its indications are decisive. 
As to its disadvantages, the only one which seems tenable is, that 
