250 Mr. Pepys’ Account of a new Eudiometer. 
to be preferred to the method with nitrous gas, as the green 
sulphate of iron does not combine with the other gases, with 
which the nitrous gas is commonly found to be contaminated, 
and more certain results are obtained. 
Having had occasion to repeat many of the experiments of 
others, and to make some new ones, I soon found what every 
one, who has been engaged on the same subject, must have 
experienced; that an apparatus more commodious than has 
yet been proposed, and at the same time capable of giving 
correct results, with the greatest minuteness, was still a desi- 
deratum in eudiometry. To detail the various ideas that pre- 
sented themselves on the subject, would be an unnecessary 
encroachment on the time of this Society : but as I at last 
succeeded in contriving an instrument, possessing the above 
properties in a very eminent degree, I flatter myself I shall 
not be thought intrusive, in offering a description of it. 
This apparatus, which is of easy construction, and extremely 
portable, consists of a glass measure M. fig. 1, graduated into 
hundred parts ; a small gum elastic bottle B. fig. 2, capable of 
containing about twice the quantity of the measure, and fur- 
nished with a perforated glass stopper S, which is well se- 
cured in the neck of it, by means of waxed thread wound 
tight round it: and a glass tube, T. fig. 3, also graduated, but 
into tenths of the formed divisons, or into thousand parts of the 
measure. 
The glass stopper, made fast in the neck of the gum elastic 
bottle, as above mentioned, has its exterior end ground with 
emery, exactly to fit the mouth of the measure ; to the lower 
end of the graduated tube T is cemented a small steel cock, 
