LEEDS CHEMISTS’ ASSOCIATION. 
419 
purposes is that devised by Mohr, of Coblenz, and consists of a tube open at both ends, 
capable of holding rather more than 1000 grains of solution, and graduated into 100 equal 
divisions of 10 grains each. To the lower opening, which is a small one, is attached a 
small tube by a piece of india-rubber tubing, which on pressure by a spring clamp of 
wire forms a very simple and effective stop-cock by which even drops can be accurately 
delivered. I have other forms here which will explain themselves. Besides the burette, 
a larger graduated vessel is required for preparing the standard solutions. This may 
either be a cylinder like the burette, only larger and graduated from 100 to 10,000 grains, 
or it may be a flask which holds 10,000 grains when filled to a mark in the neck. The 
former is better and more convenient, the latter cheaper. Two or three pipettes, or small 
dropping-tubes, which when filled to a mark in the narrower upper portion of the tube 
will deliver 100, 200, or 500 grains, are also very useful. A few flasks and beaker glasses, 
scales and weights, and a few chemicals to act as indicators, with the standard solutions, 
complete the volumetric outfit. 
Analyses that may be made volumetrically can be roughly classed under three heads, 
viz. analysis by saturation, analysis by oxidation or reduction, and analysis by precipi¬ 
tation. I will shortly describe these divisions, giving an example or two as we go on. 
The first of them, or analysis by saturation, includes, and in fact is almost constituted 
by, the important items of alkalimetry and acidimetry. It is a property of all alkalies 
that they combine with acids ; neutralizing them, or destroying their acid properties, and 
becoming themselves neutralized, or having their alkaline properties destroyed thereby. 
It is also a property of the vegetable blue colour litmus that its blue is turned to a red 
by a very slight excess of acid, and again, that this reddened litmus is re-changed to 
blue by as slight an excess of alkali. If we have then a solution of any alkali with 
which a small quantity of Tinct. Litmus has been mixed and add to it an acid, this acid 
will be destroyed and thus rendered incapable of reddening the litmus as long as there 
is any alkali present. Immediately however the alkali is all decomposed, the next drop of 
acid will redden the previously blue liquid, and thus show the end of the operation ; 
then from the number of grain-measures of acid that have been used, the amount of 
alkali present is calculated ; whether this be soda, potash, or any other. 
The principle of acidimetry is just the same as above described, only reversed: the 
litmus is added to the acid, is reddened by it, then standard alkali added till the blue 
is restored, and the result obtained by a similar calculation. As it is often required, in 
Alkalimetry[especially, to know the percentage of pure material present in a given sample, 
it is well to weigh out such a quantity as if pure would be saturated by 100 of the 
alkalimeter divisions or decerns (10 grain-measures). The number of decerns of acid re¬ 
quired then gives at once the percentage without further calculation. These cases where 
the result is obtained by direct saturation are among the simplest in volumetric 
analysis. There are many modifications of the saturating principle devised to meet par¬ 
ticular cases, into which I cannot enter in a hasty sketch like the present, and I would 
here mention that in the examples I have given or may give, I describe only the broad 
facts and as simply as I can, without at all entering into the minutiae of conditions 
necessary in particular cases. I have written this principally with a view of inducing 
those who may know but little of the subject to pursue it further. 
Before we leave acidimetry we may just notice a process which does not come under 
the head of saturation analysis, but which is useful in some cases, especially in testing 
the strength of the commercial vinegars, whose brown colour somewhat interferes with 
the observation of the change of colour in the added litmus. This is the use of ammonio- 
sulphate of copper as an acidimetric solution. Ammonio-sulphate of copper solution 
may be regarded as a solution of CuO in NH 3 , besides NH 4 0S0 3 . It is, as you know, a 
clear blue solution. If this be added to an acid, the ammonia combines with it and the 
CuO is precipitated ; this precipitated CuO is however re-dissolved by the acid as long as 
such is present, but when the acid is all neutralized the CuO is no longer re-dissolved, 
and the previously clear solution becomes turbid. The end of the operation is thus dis¬ 
tinctly indicated. 
The class of analysis by oxidation or reduction is of great importance, and its 
principle is very simple, although the processes are rather more complicated than in 
alkali or acidimetric estimations. Substances capable of combining with oxygen in 
known proportions, thus producing compounds with properties different from their original 
ones, are brought into contact with substances capable of yielding a known quantity of 
