VOL. 6, NO.9
METHODOP CHEMICAL INSTRUCTION
1527
printed on the other part of the board. Letters and figures were one and one-quarter inches high. The electrical charges carried by each radical were indicated with plus and minus signs after each formula, the number of marks indicating the valence. This chart has been used very much by the students as a help in writing formulas. The instructor has, several times during class, employed the chart as a means of instruction. The students were divided into two groups, a captain being appointed for each side. These chose their sides, and a formula "bee" was conducted. The names of compounds were called out by the instructor, first to one side and then t o the other. The contestants would give the formula, and when one missed the person missing it would take his seat. As soon as half of the members of either team were down, one of them had the privilege of answering for one of his colleagues who had just missed and, if correct, would change places with the one who had missed. This helped to keep the interest and attention of the students after they had been put down. Likewise the formula was given and the student would give the name. After some drill in this fashion the chart was covered up and the contest continued without it. This has been an exceedingly good method by which to teach formulas, names of compounds, radicals, and valences, knowledge which ordinarily has very little interest for the students, and knowledge which is sometimes neglected. There were many other projects both in form of displays and charts which have been used and are being used t o a very good advantage in the chemistry classes. Space, however, is %at afforded for discussion of all of them. However, it is hoped that some material in this article may be of value t o other chemistry instructors, even though this as presented has been very incomplete.
The Use of Chrome Leather Waste. The chemical composition of chrometanned leather waste with a water content of 50% is approximately: protein, 3 5 4 5 7 0 ; CrO 2L/1-31/2%; SOs, 1-2'12%. Hitherto this material has not been successfully utilized; glue prepared from it had a low viscosity and had color. Dr. Stadlinger (Charlottenburg) describes (Chem.-Zlg , April 18, 1928) how these difficulties have now been overmme by the use of magnesium oxide instead of alkalies in the treatment of the waste. In the processes of Rinck (Am, patent 1,612,746-1926) and of Ellenherger and Schrecker (Ger. patent 457,725--1928), the leather waste is heated to hailing point with water and magnesium oxide, with or without the addition of a little alkali. The glue-containing liquid is drawn offand concentrated. The glue so prepared has a good color and smell, is neutral, but has a rather low viscosity. Chromium can generally be detected in small amounts. The author states that if the viscosity could be increased this material would be in many respects superior t o other varieties. The use of nitrogen-containing leather waste as a manure is not advisable without first determining the chromium content. The problem of preparing chrome alum from it remains to be solved.-Chem. & I%d., 47, 1113 (Oct. 26. 1928).
