194 Breidahl and Rothera .- 



obtained, so that the invoking of the tannic acid retardation is 

 not applicable. 



We therefore maintain (i) that Ewart's tannic acid complica- 

 tions are not applicable to the experiments of Greenwood and 

 Rothera; (ii) that Ewart is incorrect in assigning the tannic acid 

 retardation to an action upon the starch; and (iii) that experimen- 

 tal results obtained under quite different conditions and with quite 

 different proportions of reagents have been used in a wholly un- 

 justifiable manner, as though applicable to Greenwood and 

 Rothera's conditions, and reagent coticentrationa. 



1. — Action of Tannic Acid on Filtered Starch Solutions. 



1% tannic acid solution was added to 1% starch solution in the 

 proportions of 1:1; 1 :-3 ; 1:7; and 1:15 respectively, the final 

 •concoctions of tannic acid being 0.5%; 0.25%; 0.125%, and 

 0.0625% respectively. They were mixed and kept at room tem- 

 perature. 



The first two gave a cloudiness immediately, which became dense 

 on standing; but after eighteen hours there was no sign of a 

 precipitate. 



The third gave a very slight cloudiness on first mixing, but this 

 became more marked on standing. 



The fourth showed no appreciable change from a control to which 

 an amount of water equal to the tannic acid solution had been 

 added, but after standing eighteen hours there was a just per- 

 ceptible difference. 



In the course of one of the expeiiments. to be described later, 

 1% tannic acid and 1% filtered starch solutions were mixed, so that 

 the final concentrations were .2% tannic acid, and .8% starch re- 

 spectively. The starch solution had been made up five days previ- 

 ously, and had not been filtered in the meantime. 



A cloudiness developed 'anunediately on mixing, which was done 

 at room temperature. 



This was then placed in a water bath kept at 38o — 4()0C., with 

 a control. At the temperature of the bath it became much cleai-er. 

 being but little denser than the control (which contained .8% 

 starch solution), and at the end of twenty-thiee hours there was a 

 slight transparent precipitate at the bottom of both tubes, being 

 slightly greater in that containing tlie tannic acid. 



