346 Wisconsin Academy of Sciences, Arts, and Letters. 
action upon the zinc could be detected by Mr. Falk. Tbe zinc 
was covered by an even white coating. Fo greater evolution of 
gas was observed near tbe platinized portion of tbe zinc than 
upon the rest of it. Magnesium, aluminum, and cadmium 
were^ not acted upon; no gas was evolved and tbe metals re¬ 
mained perfectly bright. During the experiment the hydrogen 
chloride gas passed into the benzene very rapidly. 
At 12 :28 p. m. the bottle containing the metals and the ben¬ 
zene solution of hydrogen chloride was opened to the air. 
After two minutes’ standing no action on the zinc was seen; at 
12 :31 no action on the zinc, although I shook up the benzene 
solution to distribute the moisture taken up from the air evenly 
throughout the liquid. At 12 :32%, on shaking up the solu¬ 
tion, evolution of hydrogen upon the zinc commences, but mag¬ 
nesium aluminum and cadmium remain bright for a long 
while; gradually the magnesium appears tarnished. 
As the bottle remained open to the air, up till 12 m ASy 2 zinc 
gave off gas with increasing rapidity, but thereafter less and 
less gas came from it, till at 1:12 p. m. the rate of gas evolution 
was quite slow. Up till this time the magnesium, aluminum 
and cadmium still appeared bright. 
The thought immediately occurs, that the hydrochloric acid 
was exhausted, consequently further addition of water did not 
accelerate the rate of gas evolution. But addition of a drop of 
water caused an immediate and vigorous evolution of hydrogen 
upon zinc while no hydrogen was given off from the other 
metals. The hydrochloric acid, then, was present in quantity, 
but with moisture being absorbed from the air at a steady rate 
at the surface of the benzene solution, we get first an increased 
action and then a decrease. 
The explanation of all this is at hand: The hydrochloric 
acid solution in benzene acts upon zinc, forms zinc chloride 
and this forms a protective coating upon the zinc. In this 
same paper I have shown that zinc chloride is insoluble in ben¬ 
zene; When moisture is allowed to enter the solution slowly 
no action is observed till four and one-half minutes have 
elapsed, since sufficient moisture must be present to dissolve 
