Patten i —Solutions of Hydrochloric Acid in Solvents. 347 
away the protective coating and allow the hydrochloric acid so¬ 
lution to attack fresh zinc surface. 
The tendency of zinc chloride to unite with water is well 
known. The first portions of water added, then, do not clear 
away the zinc chloride but unite with it. The latter portions 
of water dissolve off the coating, fresh zinc is acted upon and 
the zinc chloride thus formed again coats the zinc and the ac¬ 
tion ceases. 
It is worthy of note that the zinc was acted upon for a shorter 
time on Tuesday than on Monday in the experiments conducted 
by Mr. Falk. The first day the drying materials were less 
saturated with moisture than on the second day. This is why 
the action was shorter: the less moisture, the better the action 
went, since there was less chance to form the compound of zinc 
chloride and water, which is a more sticky coat than the dry 
zinc chloride. Reference to my first experiment with zinc, ben¬ 
zene and hydrogen chloride will show the excessive precautions 
taken to dry all apparatus and materials, and that the time 
during which gas is evolved from the zinc is one hour and 
twenty minutes certainly, but much longer in reality, since I 
neglected to watch the experiment to' see exactly when the ac¬ 
tion stopped, being at that time unaware of the part duration 
of action was to play in the present needs of the discussion. 
From the work of Mr. Falk, then, it appears that the action 
upon zinc of hydrochloric acid gas dissolved in benzene does 
not cease because of lack of moisture to form HC'l into H and 
01 ions, but simply because the zinc coats over and the acid 
solution cannot get at it. Mr. Falk thought this coating too 
thin to protect the zinc, but it is well known that extremely thin 
coatings serve as impervious coverings on some metals ; for ex¬ 
ample, the coat which forms upon metallic aluminum when ex¬ 
posed to the air. In fairness to Mr. Falk it should be said 
that he approached this problem from the standpoint of utility, 
wishing to perform an organic reduction under Dr. Remsen’s 
guidance. While' I have criticised severely the method used by 
him in its bearing upon this discussion, I would not be under¬ 
stood as reflecting in the least upon Mr. Falk’s efficiency as an 
open-minded, clear-thinking, painstaking chemist. 
