142 
sulphuretted hydrogen is formed. With sodium amalgam 
the action is almost instantaneous. A small quantity of 
sodium amalgam is covered in a test tube with an equal 
amount of chemically pure sulphuric acid, sp. gr. 1°84; the 
smell of sulphuretted hydrogen is at once perceived, and on 
pouring water into the test tube the solution appears milky, 
from the suspension of finely divided sulphur. But the 
course of the reaction can be better studied by employing 
zine instead of sodium amalgam, as the action proceeds 
slower and more regularly in this case. (In preparing the 
zinc-amalgam, whether the zinc be used in little sticks or in 
filings, I find it convenient to cover the mercury and zine 
with water, rendered alkaline by a drop of soda, potash, or 
ammonia. The amalgamation takes place very rapidly, and 
at a lower temperature, and the operator is not exposed to 
the noxious vapor of mercury. I prefer alkalies to acids in 
amalgamating zinc.) 
Zinc-amalgam is placed in a small H2S apparatus and 
covered with about an equal amount of chemically pure 
sulphuric acid, sp. gr. 1°84, and the gases evolved are passed 
into a solution of acetate of lead. The first few moments 
only hydrogen seems to be formed, but presently the reaction 
becomes intense, and sulphuretted hydrogen is given off in 
abundance. The liquid in the apparatus becomes white, 
which is caused partly by the formation of anhydrous sul- 
phate of zinc, and partly by the deposition of sulphur. 
There appears to be a period at which H:S and SOs, are 
formed simultaneously, and the two, reacting upon each other, 
give rise to an abundant deposit of sulphur. In the latter 
stage of the reaction, sulphurous acid alone is formed. At 
last the generating flask contains only mercury and white, 
dry sulphate of zinc; that is to say, if too much sulphuric 
acid is not taken. (An excess of sulphuric acid should be 
avoided from the beginning, as the reaction toward the end 
generally becomes very violent in this case, volatilizing mer- 
cury and sulphur, and forcing the liquid out of the flask.) 
If we pour water into the generating flask, the sulphate ot 
zinc is dissolved, and the quantity of sulphur formed becomes 
