H. Gruener — lodometrie Determination of Nitrates. 43 



the amount of reduction by arsenic acid in the residue proved 

 futile, and a distilling apparatus was found to be necessary. 

 For this purpose a small retort was used, the neck of which 

 was bent downward about two inches from the body, so that 

 the retort itself might be tipped backward, allowing the unbent 

 portion of the retort to run upward, thus guarding against 

 loss from spattering. Into the tubulature of the retort was 

 ground a glass tube drawn out at both ends to serve as a per- 

 forated stopper for the entrance of carbon dioxide. The neck 

 was passed through a rubber stopper into a side-neck Erlen- 

 meyer flask, the exit tube of which was prolonged and dropped 

 into a side neck test tube used as a trap. The retort was 

 covered with a simply contrived hood which kept the upper 

 parts warm and prevented the iodine from settling anywhere. 

 In the retort was placed the nitrate with an excess of potas- 

 sium iodide, and in the receiver a known amount of decinor- 

 mal solution of arsenious oxide strongly alkaline with hydro- 

 gen sodium carbonate and diluted to a convenient bulk. The 

 trap contained nothing but water. The phosphoric acid used 

 was at first 10 cm 3 of strong acid, specific gravity 1*7, with 

 varying amounts of water, but when it was found that the 

 amount of water present was an essential feature, a definite 

 mixture was used as designated in the tables. The acid was 

 added to the retort last of all and after carbon dioxide had 

 been passed for a sufficient length of time heat was applied. 

 The carbon dioxide was evolved in a Bonn generator from 

 materials which had been carefully boiled, and cuprous chlo- 

 ride was added to the acid in the generator to take up the 

 oxygen from any traces of air. Between the introduction of 

 phosphoric acid into the retort and the application of heat a 

 good stream of gas was passed for ten minutes, at the end of 

 which time the bubbles escaping at the last trap were com- 

 pletely absorbed in potassium hydrate of the requisite strength. 



The first experiments were in blank with no nitrate present. 

 Upon warming the mixture of phosphoric acid and 2 grm. of the 

 iodide signs of free iodine were developed, and by titration of 

 the contents of the receiver at the end, iodine to the amount 

 of "0014 grm. we s found to have been liberated, either by residual 

 traces of air or by dissociation. The experiment was re- 

 peated, but in this case all the water used had been boiled 

 immediately before the experiment and here iodine to the 

 extent of -0009 grm. only was found to have been liberated. 

 The cause and remedy for this liberation of iodine are discussed 

 presently. A series of experiments was performed to study 

 the action of the reagents when nitrates were present. 



The method of procedure was as follows : The nitrate was 

 taken for convenience from a solution of 5 grams in 500 cm 3 



