If we begin with oxygen we get a possible molecular weight of 35.3. Proceeding from this as illustrated above we get 2/3Na, '/X and 10. Since thirds of atoms are impossible we must multiply our result by three which gives the same formula obtained in the other two cases. It appears, therefore, that without abandoning the reasoning and procedure to which pupils have been accustomed in previous work in percentage we may derive the formula of the compound by the use of any one of the percentages given in the problem. The writer knows of no text which presents this method. All texts are unanimous in giving the method of dividing the percentages by the related atomic weights to get the ratios of the numbers of atoms; these ratios often do not come out as whole numbers but must be divided by the smallest one of the ratios to reduce the values to whole numbers. But to divide percentage by percentage is contrary to the rules of arithmetic as the pupil has been accustomed to think of it. Why, then, puzzle Johnny by giving him a new method for doing problems when methods already familiar will do the same work satisfactorily? To thinking teachers the question is submitted whether in the writing of chemistry texts there is anything gained by abandoning the line of reasoning and procedure which has been used in all other problems involving percentage for a method which is no simpler, gives no different answer, and is neither necessary nor more logical.
Synthetic "Perfect" Diet Gives New Vitamin Clue. The day when we will live on synthetic concentrated pills of food is yet far distant. Yet science's latest attempts t o raise laboratory animals on an artificially devised diet of pure foods have led to the discovery of the new vitamin F, recently announced by Dr. Herbert M. Evans of the University of California. When a diet of purified food elements consisting of casein and recrystallized cane sugar, certain necessary salts, and the five recognized vitamins, A. B, C, D, and E, was fed to rats in the laboratories of the department of anatomy, the animals failed to reach more than half size. Theoretically, this diet contained all the elementsnecessary for the health and happiness of rats, hut actually something else was necessary. Growth stopped altogether and the animals remained sexually immature. Natural food had to he resorted to, to supplement what might he called a chemically pure menu in order t o reawaken their growth and convert them into healthy adult animals. "Among the natural foods, lettuce and liver were the most potent," declared Dr Evans, "and they, therefore, almost certainly contain a new sixth member of the vitamins, to which designation F will be given." Lettuce when heated and dried failed to give the good results of the fresh product, the investigation showed. Dr. Evans has t o his credit also, the discovery of vitamin IS, a t one time known as vitamin X, a lack of which brings about sterility. Oil from the germ of the wheat grain is thus far the most potent source of this necessary food factor.-Science Service
