METHOD OF GOOCH AND GRUENER 453 



through g; there is no fear either of the iodid solution running 

 back, or of any bubbles of air escaping through y if this is done 

 carefully. This is a precautionary measure, in case a trace of 

 the liberated chlorin might have lodged in the comparatively cool 

 liquid in the tube h. The carbon dioxid is once more turned 

 on slowly and the liquid in A is boiled again until it is reduced 

 to about five cubic centimeters. It is now only necessary to al- 

 low the apparatus to cool, passing carbon dioxid all the time, 

 after which the contents of the condensers are transferred to 

 a flask and titrated with thiosulfate. At the end of a properly 

 conducted experiment, the glass in the upper part of tower E 

 should be quite colorless and there should be only a mere trace 

 of iodin showing in the lower part of the tower, while the liquid 

 in the last bulb of the geissler apparatus ought to be pale yellow. 

 During the operation, the stopper of A and the various joints 

 can be tested from time to time by means of a piece of iodid of 

 starch paper, and before disjointing it is well to test the escaping 

 gas (say at m) in the same way, to make sure that all nitric oxid 

 has been thoroughly expelled. 



The method is capable of giving accurate results, but it is 

 not preferable to the reduction or colorimetric processes. 



392. Method of Gooch and Gruener. The principle on which 

 this method rests depends on the decomposition of a nitrate in 

 presence of a hot saturated solution of manganous chlorid and 

 hydrochloric acid in an atmosphere of carbon dioxid. 76 The 

 products of decomposition are passed into a solution of potas- 

 sium iodid and the liberated iodin is titrated with standard sodium 

 thiosulfate. The products of the reaction are chlorin, nitric 

 oxid, and possibly nitrosyl chlorid, and under proper precautions 

 the iodin set free is quantitatively proportional to the weight 

 of nitrate decomposed. The manganous mixture is acted on 

 slowly at ordinary temperatures, but on heating, the nitrate is 

 decomposed with the formation of a higher manganese chlorid and 

 nitric oxid. When the heat is continued a sufficient length of 

 time the chlorin from the higher chlorids is evolved and only 

 manganous chlorid remains. During the heating the color of 



n American Journal of Science, 1892, [3], 44 : 117. 



