68 CARNEGIE INSTITUTION OF WASHINGTON. 



nesium sulphate and potassium nitrate. Almost as good was the com- 

 bination in which tribasic calcium phosphate replaced the dibasic form. 

 All of the cultures just mentioned were not only vigorous, but also of 

 the deepest shade of green. 



Aside from the specific results just outlined, some general indica- 

 tions derived from this work and utilizable in further experiments may 

 be mentioned : 



1. In comparative experiments the "soluble ferric phosphate" has 

 given results much more satisfactory than ferric phosphate. Citrate 

 of iron may be an important constituent of the culture solution. Ferric 

 oxalate is not satisfactory. 



2. Magnesium-ammonium phosphate is not a satisfactory source of 

 nitrogen for the variety of wheat employed, but the compound is satis- 

 factory as a source of magnesium. 



3. Using tribasic calcium phosphate as the only source of calcium, a 

 proper balance with magnesium is obtained only when the tribasic salt 

 of magnesium is used, or more soluble forms of magnesium may be em- 

 ployed if ferric citrate is used instead of the "soluble ferric phosphate. " 



4. Any of the insoluble salts of calcium and magnesium employed in 

 this work will fm-nish under the conditions an adequate concentration 

 of these ions for most favorable growth, and the problem is one of ob- 

 taining the requisite physiological balance. 



Work is in progress to determine the relation of other plants to such 

 combinations of salts as have been employed above. The concentra- 

 tion of the solutions will also be determined by the lowering of the 

 freezing-point. The initial and final hydrogen-ion concentrations 

 have been determined colorimetrically. 



Preparation of Reagents and Amino-Acids, by H. A. Spoehr and J. M. McGee. 



In the experimental work of the past three years a great deal of delay 

 and inconvenience has been occasioned by the difficulty of procuring 

 reliable chemicals. The situation has been growing constantly more 

 acute; not only has it been found necessary to purify practically all 

 chemicals, even the very simplest, but some of them have no longer 

 been obtainable at all and have had to be prepared in the laboratory. 

 This practice has naturally resulted in a great consumption of time and 

 energy. Neither the larger firms of manufactin-ing chemists nor the 

 committees of the various scientific bodies appointed to relieve the 

 situation have offered any substantial encom-agement, so that several 

 investigations have had to be greatly modified or indefinitely post- 

 poned. 



Amino-acids have not been procurable for some time or only at an 

 exorbitant price and of a quality utterly unfit for physiological work. 

 As this group of compounds is essential for a continuance of the inves- 

 tigations on respiration and certain phases of the work on biocoUoids 



