240 PHOTOSYNTHESIS 



formed.-*' Hempel -' also called attention to the fact that it is essential 

 that potassium hydroxide purified from alcohol should not be used. Con- 

 siderable difficulty has been encountered by various workers to find just 

 the right solution of potassium pyrogallate. Haldane recommends a fully 

 saturated solution of potassium hydroxide of specific gravity of 1.55. 

 The solution is made up of 1 gram of pyrogallic acid to 10 cc. of the 

 potassium hydroxide specific gravity 1.55. However, at lower tempera- 

 tures this solution is apt to solidify which may cause a great deal of 

 trouble in the apparatus. The solution is the most efficient oxygen 

 absorbent thus far recommended. The directions given by Benedict ^* 

 for a slightly more dilute solution have proven very trustworthy: "A 

 solution of potassium hydroxide was prepared by dissolving 500 grams 

 of stick potassium hydroxide, not purified by alcohol, in 250 cc. of water. 

 Usually the specific gravity of the resulting solution was 1.55. During 

 the progress of this research, several shipments of stick potassium hy- 

 droxide were used, and the varying water-content of the chemical is 

 shown by the fact that it was frequently necessary to add more potas- 

 sium hydroxide to bring the solution to the desired density. To 135 cc. 

 of this saturated solution was added a solution of 15 grams of pyrogallic 

 acid in 15 cc. of distilled water. . . . 



"This solution takes up oxygen rapidly and has a high absorptive 

 capacity. It has been assumed that since the solution was so much more 

 concentrated than Hempel's, his assertion that no carbon monoxide was 

 developed with his weaker solutions held true in this case also, par- 

 ticularly as Haldane states that with his extremely concentrated solu- 

 tion no traces of carbon monoxide are found. Furthermore, certain 

 evidence here presented seems to supjxDrt this view. When a known sample 

 of air is analyzed a number of times, the percentage of oxygen at the 

 beginning of the series does not differ from that found at the end even 

 when as many as 30 analyses are made with the one charge of potassium 

 pyrogallate. It seems reasonable to suppose that if carbon monoxide 

 were formed, a somewhat different amount would be produced after 

 the first, second or third analysis than after the twenty-eighth or twenty- 

 ninth. On the other hand, it is not impossible that in the production of 

 carbon monoxide there may be an extremely small quantitative relation- 

 ship between the oxygen absorbed and the disintegration of the pyrogallic 

 acid, so that the carbon monoxide given off may remain strictly pro- 

 portional to the amount of oxygen consumed. Since in each of these 

 analyses exactly the same amount of oxygen is absorbed, there still 

 may be a slight constant factor present ; consequently, it is necessary to 

 take into consideration the fact that in all of these analyses there may 

 be traces of carbon monoxide produced. In that case the tendency 



* Boussingault, J. B., Compt. rend.. 57, 885 (1863). 



"Hempel, W., Ber. chem. Ges., 20, 1865 (1887). Tacke, B., Archiv. fuer die 

 Gesammte Physiol. 38, 40 (1886). 



^ Benedict," F. G., Carnegie Inst, of Washington, Pub. No. 166, p. 80 (1914). 



