296 Annual Report of the Council. 



advantage, that an almost insoluble sodium oxalate 

 is formed, and thus the excess of alkali and all the 

 bye products can be easily separated. For a successful 

 operation of the process it was necessary to bring the 

 recovered mixture of the alkalis quickly into work again, 

 which could be only done by having a rapid method 

 for determining their relative amount. A series of experi- 

 ments led Dale to a very simple method of analysis. 

 A given volume of the solution is neutralized with tartaric 

 acid of known strength, and then an equal volume of the 

 latter is added in order to convert the alkalis into the 

 bitartrate, that of potash separating out and the separation 

 is quickened by stirring the liquid well. In order to get 

 good results the solution of the sodium bitartrate must be 

 nearly saturated or stand at 6° Tw. The cream of tartar 

 which separated out was filtered off, slightly washed 

 with water, and filtrate and precipitate were then separately 

 neutralised with a standard solution of caustic soda. Thus 

 the percentage of the two alkalis could be ascertained 

 within half an hour. Dale, as usual, did not publish this 

 method, and many years afterwards it was rediscovered by 

 Mohr. 



The same was the case with another analytical method 

 which Dale devised for estimating the amount of colouring 

 matter in indigo, which is called indigo blue and has the char- 

 acteristic property of being converted, by reducing agents, 

 into indigo white, which is soluble in alkalis. On exposing 

 this solution to the air, it rapidly absorbs oxygen, and indigo 

 blue is reprecipitated. This reaction is made use of in 

 indigo dyeing, fine indigo being brought together with water, 

 green vitriol, and slaked lime. A careful examination of 

 this subject by Dale showed that a certain quantity of 

 indigo blue undergoes such a change that it is not repre- 

 cipitated, and in employing this reaction as an analytical 

 method, this has to be taken into account. By a series of 



