612 STATE BOARD OF AGRICULTURE. 



less economical so far as time is concerned, require apparatus not al- 

 ways available, and technic with which laboratory workers are not 

 usually familiar. 



In the "titration method" of Patten and Marti (41) is found one 

 which is as adaptable to any laboratory as is McCandless' (37) (38) 

 method and which has the advantage over that method in that it can 

 be performed in somewhat less time. It will be discussed later in detail. 



Hall (24) has suggested the use of the solid salt for the preparation 

 of the reagent. Theoretically this scheme is above reproach and might 

 to some degree be practically successful in the hands of men who could 

 acquire sufficient experience in the preparation and handling of the 

 salt. In one or two trials which we made we were unable to obtain 

 satisfactor}^ results, the salt always losing ammonia and yielding a 

 solution of too high a hydrogen ion concentration. This statement should 

 not be construed as a finally adverse criticism of Hall's suggestion. 

 Could we have spent more time on it we could undoubtedly have checked 

 his results, but we feel that our experience teaches conclusively that the 

 solid normal triammonium citrate is too unstable a substance to be relied 

 upon for use by the average laboratory worker for the preparation of 

 the reagent in question. 



Finally in this group of methods may be mentioned the colorimetric 

 method of Eastman and Hildebrand (15). Of all those which have been 

 proposed this one appears to be the most desirable. It is the equal 

 of any in accuracy, requires no apparatus not found in any laboratory 

 and the whole adjustment process can be performed with one or more 

 titrations, depending upon the accuracy with which the operator ap- 

 plies the results of the first one. While the writer has certain suggestions 

 to make whereby he thinks that this procedure may be still further im- 

 proved, he nevertheless feels that in the form in which it was proposed 

 by its originators it is superior to all others. 



(c) Methods for the preparation of solntiops icith empirical com- 

 positiojis: This class of methods requires but little comment. Such 

 methods are wholly emj)irical in nature, usually involve the securing 

 of a neutral solution first and so far as the writer is aware occupy no 

 place in present day methods. 



In some biochemical work involving the determination of hydrogen 

 ion concentrations the write]- had occasion to make use of the methods 

 devised by Clark and Lubs (10) for tbe preparation of bacterial culture 

 media. It occurred to him that these methods could be applied equally 

 well to the control of ammonium citrate solutions as had already been 

 done in principle by Eastman and Hildebrand (15). The only dif- 

 ferences between the method of the latter investigators and the one to 

 be described are in the indicator and the standard solutions used, . 



changes which however seem to greatly increase the accuracy and ease 

 of manipulation of the process. 



Both methods are based upon the scheme for determining coloii- \ 



metrically the liydrogen ion concentrations, i. e., the reactions of solu- \ 



tions. In brief, this consists in preparing a series of solutions whose *" 



compositions fix their reactions which originally are detoi-mined electro- 

 metrically; adding to definile <|nantities of these solutions eqiml quan- 

 tities of a suitable indicator and comi)aring with them the color produced 

 by an equal concentration of the same indicator in the solution to be 



