Patten—Solutions of Hydrochloric Acid in Solvents. 351 
formation of a protective coating upon all the zinc was seen, 
not a mere tarnish but a thick white coat. 
At 10 :04—22 minutes from the start—there was still a de¬ 
cidedly brisk evolution of gas upon all the zinc. 
At 10:10—28 minutes—less gas was coming off. 
At 10:20—38— minutes—very slow evolution of hydrogen. 
By shaking the flask about and getting a fresh zinc surface by 
abrasion of one piece of metal upon another, gas was again 
evolved upon all the zinc in spots, not uniformly, showing that 
the zinc ceased acting because of this protective coating and not 
because there was an insufficient quantity of water present to 
“ionize” the hydrochloric acid. 
At 10:30 gas still came slowly from all the zinc in spots 
showing that where the coating was open the acid solution 
acted upon the zinc. The coating upon the zinc is thicker. 
At 10 :40 gas coming from all the zinc at intervals of about 
20 seconds between bubbles. 
At 11:00 minute bubbles from all the zinc at long intervals. 
At 1:45 p. m. gas still coming slowly in tiny bubbles from 
all the zinc. 
At 3 :18 p. m. gas was evolved in small bubbles at long inter¬ 
vals, on all the zinc. Confirmed by G. M. Wilcox of Armour 
Institute and L. Kahlenberg. 
At 5 p. m. all the zinc was covered with a thick even coating 
of white zinc chloride, which could not be dislodged by shaking 
the metals together, since no further action of zinc on the acid 
solution could be detected. 
During all this time a slow steady current of hydrogen chlo¬ 
ride was passed into' the benzene. The magnesium is not acted 
upon, so far as could be detected by use of a large hand lense, 
either as to' gas evolution or diminution of lustre, after seven 
days’ contact with the acid solution. In view of the important 
part which thin films play in the corrosion of metals it would 
be advisable to- subject the magnesium, and aluminum to the 
more delicate optical methods while in contact with this acid 
solution. So' far as my observation goes the magnesium is not 
acted upon. The reason for this lack of action appears to me— 
