38 BOTANICAL GAZETTE [JANUARY 
division passing to the right. It will be observed that the five 
copper salts, the nitrate, formate, acetate, chlorid, and sulfate, 
dissolved in pure water have approximately the same toxic value, 
the variation (0.00004 ) being within the limits of experimental 
error. These five salts are fatal to CE docephalum in 0.00020- 
0.00024 ” concentration in twenty-four hours. This is about a 
0.005 per cent. solution of the crystallized salt, CuSO,.5H,O, or 
one part crystallized salt to 20,000 parts water. ~ 
The addition of glycerin, glucose, or cane sugar failed to 
cause any pronounced decrease in toxic properties. The addition 
of salts like K,SO,, KCl, etc., however, caused a very great 
reduction. One part CuSO, to 20,000 parts pure water is fatal 
to CEdocephalum in twenty-four hours. It requires sixty-one 
parts CuSO, to 20,000 parts of a 5 per cent. K,SO, solution. 
to have the same effect. That the lessening of the toxic value 
here was not due to a lessening of the rapidity of the pene- 
tration of the copper salt is shown by the last three lines of 
fig. 3, where the cultures after standing ten days showed a toxic 
value of less than one-fortieth that of the CuSO, in pure water. 
A test made by adding a small quantity of KCl to solutions of 
CuCl, gave an increase in the toxic value of the mixture. Further | 
experimentation on this point is needed, but the indications are — 
that here we have a similar phenomenon to that observed on the 
addition of chlorids to mercuric chlorid solutions," small additions 
of a chlorid Causing an increase, and larger amounts causing 4 
decrease in toxic properties; the former probably through the 
formation of highly toxic ~HgCl> ions, and the latter through 
the formation of K, HgCl, double salt molecules having a low — 
toxic value. Copper reacts very similarly to mercury in respect ? 
to the formation of double salts with alkali chlorids.227 These — 7 
double salts would naturally be highly dissociated into metallic : : 
cations and the anion ~CuCly, and similar anions. That the — 
ion ~CuCl> should have a high toxic value is very probable, — 
being in harmony with all at present known regarding toxi¢ 
* CLARK, J. F.: Jour. Phys. Chem. 5: 289-316. 1900. 7 
* REMSEN, IRA: Inorganic chemistry (advanced course) 589. 1892. 
Sen 
