64 EXPERIMENT STATION BECOEt). 



and is not easily washed off. Soluble cliromates do not poison plants to the 

 extent arsenic does. 



" Lead chromate is made by dissolving in one lot of water potassium bichro- 

 mate, in another lot of water lead acetate, or nitrate. The two solutions are 

 mixed and a dense yellow precipitate of insoluble lead chromate is formed, and 

 potassium nitrate or acetate. The latter is soluble and is readily washed out 

 of the precipitate." In practice 2 oz. of lead nitrate combines with 1 oz. of 

 potass'um bichromate, giving 2 oz. of lead chromate. This is the amount re- 

 quired for 4 gal. of water at full strength or for S gal. of water at the usual 

 strength. 



FOODS— HUMAN NUTRITION. 



Calcium, magnesium, and phosphorus in food and nutrition, H. C. Sher- 

 man, A. J. Mettler, and J. E. Sinclair ( U. 8. Dept. Agr., Office Expt. Stas. 

 Bui. 227, pp. 70). — This report, which supplements an earlier bulletin on iron 

 and its function in nutrition (E. S. II., 19, p. 5S), includes a general discussion 

 of the subject under consideration and a summary of earlier literature, together 

 with the results of 6 experiments with man on the metabolism of calcium, 

 magnesium, and phosphorus, and a study of the amount of these mineral con- 

 stituents in typical American dietaries. 



Although the results with iron tended to confirm the common assumption 

 that a diet containing liberal amounts of protein will probably furnish at the 

 same time at least adequate amounts of iron, evidently " it can not be assumed 

 that liberal quantities of protein involve adequate amounts of all of the ash 

 constituents. As a rule the dietaries rich in protein are also fairly high in 

 phosphoric acid^ but the parallel is not nearly so close here as in the case of 

 protein and iron. With calcium and magnesium the discrepancies are greater, 

 and it can hardly be said that the amounts of these elements run even approxi- 

 mately parallel to the amounts of protein in the 20 dietary studies which have 

 been compared and which are believed to be fairly representative of the food 

 habits of people of at least the eastern half of the United States. In view of 

 these figures it can no longer be assumed that the amount of protein in a 

 dietary is a sufficient measure of its richness in ' building material.' Aside 

 from nitrogen, the elements of ' building material ' which appear to require 

 special attention in dietaries are iron, phosphorus, and calcium." 



The outline given in the bulletin of the distribution and functions of phos- 

 phorus and calcium compounds, as the authors point out, while necessarily in- 

 complete, is yet sufficient to show the great importance of these compounds 

 in the nutritive processes and to emphasize the necessity for adequate supplies 

 in the food. 



" Of the various classes of phosphorus compounds found in food, the organic 

 combinations appear in general to be of greater nutritive value than the inor- 

 ganic forms, and it is probably for this reason that different experiments indi- 

 cate quite different amounts of phosphorus as necessary for the maintenance 

 of equilibrium in man. From the results here obtained, as well as from the 

 average results of experiments by other observers, it would appear that a 

 healthy man, accustomed to full diet of the ordinary mixture of animal and vege- 

 table food materials, requires for the maintenance of his ordinary store of phos- 

 phorus compounds about 1.5 gm. of phosphorus, or nearly 3.5 gm. of phosphoric 

 acid, per day, though under special conditions or with a specially selected 

 dietary equilibrium may be maintained on much less. Many of the dietary 

 studies show so much less than 3.5 gm. of phosphoric acid per man per day 

 as to raise a question whether these people may not have been undernourished 



