VOL.
9, No. 5
CORRESPONDENCE
941
PREPARATION OF RHOMBIC SULFUR CRYSTALS DEAR EDITOR: It is well known that the size of crystals formed from a solution depends upon the rate of evaporation of the solvent: slow evaporation producing large crystals. In order to obtain large crystals i t is necessary only to prolong the period of evaporation. In the case of sulfur, proceed as follows: dissolve in 20 cc. carbon disulfide as much powdered roll sulfur as possible. Filter through a dry filter paper into a small flat-bottomed glass dish. Cover the dish with two or more layers of hlotting paper, the sheets being large enough to extend completely over the top of the dish. Lay a book or other heavy flat body on the top of the blotting paper. Set the dish away in a cool place for a week. Under the above conditions, evaporation must proceed very slowly and crystals half an inch long may he obtained. The general shape may readily be observed and the angles and beveled sides easily seen through a lens, but i t is not a simple matter to get perfect large crystals. For exhibition purposes, the smaller but more perfect sulfur crystals may be shown behind a good reading glass of high magnification so arranged from the viewpoint of the observer as to focus upon the crystals. The dish in which the crystals formed should he supported a t the eyelevel and so that the bottom of the dishjs in a vertical position. The crystals adhere to the bottom of the dish and will not fall off. A suitable P label should be appropriately attached. The above might serve as a project-"A Study of Crystallization as Affected by Timew-the two samples, large and small, being shown side by side. CHARLESH. STONE MEMOKIAL Hrcn SCHOOL BOSTON,Mass.
A SIMPLE METHOD FOR CALCULATING THE PROPORTIONS -- . - - OR .VARIOUS SUBSTANCES OF KNOWN COMPOSITION TO GIVE A MIXTURE OF DEFINITE COMPOSITION DEAREDITOR: Pharmacists, chemists, many factory workmen where chemical processes are used, teachers and workers in the field of science in general (either for the purposes of instruction or for their own use in laboratory work), as well as all others who wish to mix various quantities of materials of known composition of any one ingredient to obtain a material of certain definite composition will find the following simple method a great help in cal-
