400 BOTANICAL GAZETTE [ DECEMBER 
range, particularly with copper sulfate, in which most spores 
were killed at ;%,,. Some injury was done my rssoy Dut some 
spores grew in even so strong a solution as ,7, 
A general survey of the tables will wee that the following 
list of chemicals may be selected as having aaetnee no toxic 
action unless in great strength, as they were tried at .%, with no 
toxic action, and this was in every case greater hae: a % per 
cent. solution: K,Mn,O,, MgCl,, NH,Cl, BaCl,, MgsO,, 
Na(C,H,0,), KBr, KI, NH,NO,, NaCl, C,H,O. 
e HYDROLYTIC DISSOCIATION. 
Salts in aqueous solution present certain deviations regarding 
the changes of freezing and boiling point (and also other optical 
physical, and chemical deviations) which are not in accord with 
the general laws for solutions containing the number of molecules 
theoretically supposed to be present. ‘‘Thus a solution of KCl + 
100 H,O, instead of showing a lowering of vapor pressure of 
.OI as required by the law, shows a lowering of about double 
this. Solutions in alcohol behave like other substances and give 
normal diminution of vapor pressure.”’4 _ In general the behavior 
of such aqueous solutions of salts, bases, or acids is such as 
might be expected if they contained more molecules than their 
formula indicates. 
These phenomena led Arrhenius: to the conclusion that each 
molecule or some of the molecules are separated into part mole- 
cules or ions, a term long used by the physicist. 
According to this theory of hydrolytic dissociation a solution 
of mercuric chlorid does not consist of water and molecules of 
mercuric chlorid, but does consist of water containing ions of 
mercury and ions of chlorin, designated as Hg+ and Cl~ , accord 
ing as the element is electro-positive or electro-negative in 
electrolytic dissociation. 
Careful distinction should be drawn between an element in 
the condition of dissociation and in a molecular condition. Thus 
4OsTWALD : Solutions, trans. by Muir, p. 187. 
5 Zeits. f. phys. Chem. 1: 631. 1887. 
