380 1. K. Phelps — Combustion of Organic 



stance might be effected by determining the amount of chromic 

 acid used in the operation, taking into consideration the 

 products of combustion. This can be readily accomplished by 

 taking a weighed amount of pure potassium dichromate as the 

 oxidizing agent and determining, at the end of the operation, 

 the amount of chromic acid left by treatment of the residue 

 with hydrochloric acid, absorption of the chlorine evolved in 

 an alkaline arsenite of known strength and titration of the 

 excess of that substance with decinormal iodine solution. 



To test the accuracy of the determination of chromic acid 

 under these conditions of analysis, weighed portions of pure 

 fused potassium dichromate were introduced into a Yoit flask, 

 whose outlet tube was sealed to the inlet tube of a Drexel 

 wash bottle, the outlet of which, in turn, was sealed to a Will 

 and Yarrentrapp absorption apparatus. An amount of hydro- 

 chloric acid, more than enough to completely reduce the chro- 

 mate (15-40 cm3 of the strongest acid), was added with 20 cm3 of 

 strong sulphuric acid and the total volume made up to 

 120-1 40 cm3 of liquid. The sulphuric acid used here was puri- 

 fied from carbonaceous matter (as in the carbon determination 

 above) by heating with a few crystals of potassium dichromate, 

 the excess of which was reduced by holding the acid at a fuming 

 point for about two hours, when a portion diluted with water 

 gave no color with potassium iodide and starch paste. Pure 

 arsenious oxide, in amount slightly in excess of that required 

 to take up the oxygen to be given up by the chromate, was 

 dissolved by the aid of heat in a solution of pure sodium 

 hydroxide, taken in such quantity as to more than neutralize 

 the arsenious acid and the hydrochloric acid used to reduce the 

 chromate, and this solution was introduced into the Drexel 

 wash bottle. The flask was then connected with the wash 

 bottle, using a thick solution of metaphosphoric acid to lute the 

 joint between the flask and its stopper. The absorption appa- 

 ratus was charged with a dilute solution of sodium hydroxide. 

 Carbon dioxide was generated in a Kipp generator by the action 

 of hydrochloric acid on marble and purified from reducing 

 matter by bubbling through a strong solution of iodine in 

 potassium iodide and finally washed with a solution of potas- 

 sium iodide alone. A slow stream of this purified carbon 

 dioxide was allowed to enter the inlet tube of the Yoit flask, 

 the contents of which were then boiled. When a concentra- 

 tion to a volume of 30-40 cm3 was reached, the boiling was dis- 

 continued and, after cooling and disconnecting the flask, the 

 contents of the receiver were made acid with sulphuric acid 

 and then alkaline with acid potassium carbonate, when the 

 excess of arsenite was determined by titration with decinormal 

 iodine solution. Sometimes during the reduction of the chro- 

 mic acid, the red fumes of the chlorochromic anhydride volati- 



