276 MICRO-CHEMICAL REAGENTS. 
solution of 3 parts of iodine and 8 parts of potassium iodide in 
1,200 parts of water. After some time, a little hydriodic acid is 
formed in this solution; the deportment of the solution is then 
(for example, with starch; see page 122) not precisely the same 
as when the freshly prepared solution is used. 
26. Iodine Tincture. A solution of 1 part of iodine in 10 
parts of alcohol of the specific gravity 0.830. 
27. Iodine with Glycerin. A mixture of 1 part of iodine 
solution (No. 25) with 10 parts of glycerin of the specific gravity 
1.230. 
28. Iodine with Chloride of Zine. In 100 parts of a solu- 
tion of chloride of zinc of the specific gravity 1.800 are dissolved 
6 parts of potassium iodide and as much iodine (about 1 part) as 
the liquid is capable of taking up. 
Pure cellulose—though not that of the fungi—assumes with 
the chloride of zinc and iodinea violet color (chloride of zinc 
causes the formation of amyloid). Cells containing tannin as- 
sume with the chloride of zinc and iodine a reddish color. 
29. Potassio-mercuric Lodide (a solution of mercuric iodide 
in potassium iodide) is prepared by dissolving 1.35 paris of 
mercuric chloride (corrosive sublimate) and 5 parts of potas- 
sium iodide in 100 parts of water. Nearly all the alkaloids are 
precipitated by this reagent from their solutions, even when 
highly diluted, so that it affords indications of the presence of 
such substances. The precipitated compounds are mostly 
amorphous, and only a few assume a crystalline form after some 
hours. | 
30. Ferrous Sulphate (Green Vitriol), prepared in the 
form of a fine powder, by precipitating it from its solution in 
water by means of alcohol, and quickly drying it by exposure to 
the air. When used, 1 part is freshly dissolved in 20 parts of 
water. Many substances of the class of tannins are colored by 
this salt, but usually of a different tint than by ferric chloride. 
The addition of lime-water to sections which have been impreg- 
nated with a solution of ferrous sulphate and poring or os 
= _ rinsed with water, often produces new colorations. : 
a Ferric Chloride, The officinal solution [Pharm. Germ. ] 
