other a tube which extends not more than half an inch beyond the inner surface of the stopper. Connect one of these to a hydrogen generator; when a test shows that all air has been expelled from the apparatus heat the material in the test tube until i t is completely reduced to metallic copper. Allow the tube to cool, while the stream of hydrogen is still passing through it, and weigh it again. The data may be recorded in the following manner: 1 . Weight of test tube and cup& bromide.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2. Wcight of test tuhc and cuprous hromidc.. . . . . . . . . . . . . . . . . . . . . . . . . . . . 3. Weight of test tuhe and copper.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4. Weight of bromine in the cupric bromide.. . . . . . . . . . . . . . . . . . . . . . . . . . . . 5. Weight of bromine in the cuprous bromide.. . . . . . . . . . . . . . . . . . . . . . . . . . . (i. Ratio of the two amounts of bromine (4 divided by 5 ) . . . . . . . . . . . . . . . . . .
This experiment has been submitted to a group of sixteen students in general chemistry a t the University of Illinois-three of them obtained very unsatisfactory results due t o faulty weighing or spilling part of the sample; the other thirteen obtained ratios varying from 1.03 : 1 to 2.00 : 1, the average being 2.03 : 1. The directions as given to this class specified that the hydrogen delivery tuhe should reach nearly to the bottom of the test tube. In following these directions most of the students allowed the copper oxide to come in contact with the delivery tube, to which a little of it adhered. This error, which accounts for the high results obtained, may be avoided by following the directions given here. Some of the students completed the experiment in a two-hour laboratory period; most of them, however, did not quite finish it in that time. The time required for the completion of the experiment may be somewhat shortened if adequate ventilating facilities are provided for, in that case, the hromine and nitric acid fumes may be allowed t o escape into the hood. It will be seen that by weighing the empty test tube, the weight of copper may be found, and the experiment may be made to illustrate the law of combining proportions as well as the law of multiple proportions; if the tube is weighed after the ignition of the nitrate to oxide, the combining weights of copper and bromine may be calculated in terms of that of oxygen. I t is difficult to introduce these additions, however, without obscuring the main point of the experiment. The author wishes to express his indebtedness to Mr. Julius White for conducting the class experiments, and for several valuable suggestions.
Poison Bottles. A special type of bottle for poisons, which cannot he mistaken even in the dark, is being produced in both England and Germany. The hottlc i? rovcred with sharp protuhcranccs.
