MODIFICATIONS OF THE KJELDAHL PROCESS 355 



by decantation, and finally dry it between filter-paper. The starch 

 is then suspended in water with the aid of heat. Such a solu- 

 tion will keep for an indefinite time if it be saturated with com- 

 mon salt. Ten grams of this starch are dissolved in 1,000 cubic 

 centimeters of ammonia-free water and one or two cubic centi- 

 meters used for each determination. 



312. Modifications of the Kjeldahl Process. It would be im- 

 practicable here to give even a summary of the many unimportant 

 changes which the moist combustion process has undergone since 

 the first papers of its author were published. These changes may 

 be divided into three classes ; viz. : 



i. Those changes which refer solely to the quantities of sub- 

 stance used for analysis, to the composition of the acid mixture, 

 to the duration of the digestion, to the form and size of the flasks, 

 both for digestion and distillation, and to the manner of distilla- 

 tion and of titration. For references to the papers on these sub- 

 jects the reader may consult Fresenius. 1 The most important 

 of these minor changes are the following: Instead of the titra- 

 tion by means of separated iodin most chemists have had recourse 

 to the simpler method of direct titration of the excess of acid by a 

 set solution of an alkali. Ammonium, barium, sodium, and potas- 

 sium hydroxids are the alkaline solutions most employed. This 

 process permits of a larger quantity of the sample being taken for 

 combustion and of the use of a larger quantity of acid in the re- 

 ceiver. It also implies the use of a larger digestion flask. In fact, 

 it is now quite universal to make the digestion in a special glass 

 flask large enough to be used also for the distillation. This 

 saves one transfer of the material with the possible danger of loss 

 attending it. 



In the distillation it is a common practice, especially in Ger- 

 many, to do away with the condensing worm and to carry a long 

 glass tube from the distilling flask directly into the acid in the 

 receiver. The only inconvenience in this method is the heating 

 of the contents of the receiving flask, but this is attended with 

 no danger of loss of ammonia and the distillate, on account of 

 the high temperature it acquires, is left free of carbon dioxid. 

 1 Zeitschrift fur analytische Chemie, 1883 to date. 



