5. Difference between the temperature of the gas and that of the air in the room.
6. Errors in weighing.
7. Want of accuracy in the weights and scales.
344. Hydrogen.
Experiment 135.—Weigh 5g, or less of sheet or granulated Zn, and put it into a small flask provided with a thistle-tube and a delivery-tube. Cover the Zn with water, and introduce through the thistle-tube measured quantities of HCl, a few cubic centimeters at a time. Collect the H over water in large flasks, observing the same directions as in removing O. Weigh the water, compute the volume of the gas, reduce it to the standard, and obtain the weight, as before. Should any Zn or other solid substance be left, pour off the water or filter it, weigh the dry residue, and deduct its weight from that of the Zn originally taken. Suppose the residue to weigh 0.5g. Make and solve the proportion from the equation:-
Zn + 2HCl = ZnCl2 + 2H. 65 2. 4.5 x.
Compute the percentage of errcr, as in the case of O. If the purity of the HCl be known, i.e. the weight of HCl gas in one cubic centimeter of the liquid, a proportion can be made between HCl and H, provided no free HCl is left in the flask. State any liabilities to error in this experiment.
PROBLEMS.
(1) A gas occupies 2000cc.when the barometer stands 750mm. What volume will it fill at 760mm?
(2) At 750mm my volume of O is 4 1/2 liters. What will it be at 730mm?