702 Report of the Consulting Engineers on the Trials of 
specially-constructed stands. In this framework are supported a pair of 
tubes, A and B, connected at their lower ends by a breeches-piece to an india- 
rubber tube M, which unites them to a vessel of mercury K suspended by a 
cord passing over a pulley and balanced by the weight L. The tubes A and 
B are surrounded by water-jackets, for the j^urpose of maintaining a constant 
temperature throughout the aualj'sis — a very important point, because it 
eliminates the tedious calculations necessitated by the changes of volume due 
to changes of temperature. The tubes and their jackets are of glass. The 
tube B is graduated, and a small spirit level 0 slides up and down on a pair 
of wires in front of the tubes, and enables the mercury to be set exactly level 
in the two tubes, and as tube A is open to the atmosptiere, the pressure in B 
must be the same when the mercury columns are level. C is an inverted 
bell tube dipping into a beaker of caustic potash. E is an inverted bell tube 
containing hydrogen. D is a similar inverted bell tube which covers a pair 
of platinum poles, by means of which the water contained in the beaker can 
be decomposed by means of a current of electricity produced by a battery of 
six small cells, which also serve to send an electric spark by means of a 
Rhumkoif coil through the top of the tube B. Cocks F, G, H, I, J, govern 
the various tubes. 
The mode of operating is as follows : — The mercury vessel K is hoisted 
till the tube B is full of mercury, the gas to be analysed is connected to the 
tube N — corresponding to tube I, Fig. 1 ; the cock F is opened, the cock G 
being shut, the vessel Iv is depressed, lowering the mercury in the tube B, 
until sufficient gas has been drawn in; the cock F is then closed, and 
the vessel K is manipulated till the mercury in tubes A and B stands 
at the same level ; the volume in B is then read off. Cocks G and H 
are next opened, the mercury vessel K hoisted, and the gas is passed into 
the bell tube C, where the carbonic acid gas is absorbed by the caustic potash. 
After a minute or two the gas is drawn back into the tube B, where the 
volume is measured ; the gas is then returned into C, and left another minute 
or two to make sure that all the carbonic acid has been absorbed. It is 
then returned to B, and the volume measured again, and if there be no 
change, the absorption has been perfect and the volume of carbonic acid 
has been measured. Next, cocks H and G are closed, some water is decom- 
posed in D, and a small iiortion of the explosive mixture is allowed to flow 
into B, when it is exploded by means ol the electric spark, and by that 
means any carbonic oxide present is burned at the expense of the free 
oxysen associated with the excess of air which is generally found in the 
pioducts of combustion. The gasrs are again passed into C, and the carbonic 
acid generated by the explosion absorbed; the gas is then returned to B, 
the volume measured, and by that means the vulume of carbonic oxide 
determined. Next a measured quantity of hydrogen from E is passed into 
B, and the mixture fired. By this means the remaining free oxygen is 
removed, the volume remaining measured, and the quantity of oxygen and 
nitrogen, and therefore of air, is determined. The hydrogen in » the coal 
combining with the oxygen of the air does not appear in the products, but 
can be estimated from the volume of nitrogen. 
The description given above may seem tedious, but the 
working of the apparatus is exceedingly simple, and we fre- 
quently witnessed the completion of an analysis in the engineer's 
office in about one-quarter of an hour — in fact, Mr. Stead was 
often able to announce the composition of the waste gases before 
the run during which the sample was taken was complete. 
Table No. XII., page 7o2, furnished by Mr. Stead, gives the 
