Mr. Pepys’ Account of a new Eudiometer. 257 
composition of carbonaceous substances, lime water will be 
found sufficient. 
If it is required to know the purity of the oxygene gas, after 
the carbonic acid gas has been absorbed, the best method and 
the least liable to error, is to withdraw the residual oxygene 
gas, by means of the small graduated tube before described. 
To do this, remove the measure into the small cistern of 
mercury ; press the quicksilver out of the small bottle by the 
fingers and thumb, and let the tube rise a sufficient height 
within the measure, that the bottle extending itself shall with- 
draw the whole of the gas from the measure, taking care that 
the cock be stopped as soon as it has completed it, and also 
to prevent the solution from entering the tube. 
If the opening of the tube is small, it may then be drawn 
down into the mercury, without the possibility of any portion 
of the gas escaping, while the measure is dried or cleaned, or 
a fresh one filled with mercury supplied to receive it. 
This way of transferring will be found very advantageous, 
particularly in the separation of gases, liable to be absorbed 
under certain temperatures, and also where a new series of 
re-agents are to be employed, as from the depositions of 
former solutions on the glass measure, a source of consider- 
able error would arise. 
The residual oxygene gas being thus transferred into a clean 
dry measure, the processes before described for examining 
oxygene gas may be then used ; or the quantity of carbonic 
acid gas (for examination ) being found by lime water, another 
measure of the gas may be tried, first with the green sulphate 
of iron impregnated with nitrous gas, and then with the green 
sulphate in solution only : these will take up both the carbonic 
