any right to expect; for the method of analysis, or rather the method of taking the specimens of gas for analysis, adopted by Mr. Bell, does not admit of perfect exactness.

Although the results given by Mr. Lowthian Bell are the means of several specimens, it cannot be admitted that specimens taken almost instantaneously really give the true composition of the gas of a blast furnace. Ebelmen himself said, in speaking of the analysis of the gases at Seraing, "We must conclude from this that the analysis of the escaping gas of the furnace does not represent the mean composition of the gaseous current.”* And yet Ebelmen looked only to taking the means of the different gaseous currents at a given instant, whilst in order to have a clear idea of the working of a blast furnace, not only must we have the exact mean of all the currents escaping at a given instant, but of the true mean of a period of several hours. This important point has not been realized by any of the apparatus hitherto employed, and in taking specimens the following system is therefore proposed.

§ 9. A method of taking specimens securing a mean of all the gases during several hours.

This system is borrowed from the researches of MM. Scheurer-Kestner and Ch. Meunier on the products of combustion of coal.*

In order to obtain an exact mean a certain volume of the

total gaseous current which passes from the top of the furnace to the boilers or heating stoves, etc., is drawn off continuously during several hours, and as it would be impracticable

* Annales des Mines, t. xix. 4a série, p. 127; also Note I. Appendix. + Bulletin de la Société Industrielle de Mulhouse, 1868.

to collect the totality of the gases thus drawn off, a certain fraction is withdrawn in the same manner and continuously into a Mariotte's jar filled with mercury, containing about 3 litres. follows:

The general arrangement of the apparatus is as

Into the main pipe, which carries off the gases, there is passed a copper tube m n of 1 centimetre in diameter to 12 centimetres (a half-inch tube), fig. 13, of a length about double the diameter of the main pipe in question. The part inside the main pipe has a slit throughout that length, as at p. q, about a millimetre wide ( inch). This allows of the gases being drawn uniformly from every part of the current. The part of the copper tube outside the main pipe passes through a refrigerator on Liebig's system. Lastly, the extremity of the tube communicates by means of an Indiarubber junction with the leaden pipe which serves as exhaust. This is composed of a kind of trompe a b, provided with a cock, which allows of the current of water being regulated, and with a branch c d of greater or less length, according to the locality. This latter is soldered to the vertical tube a b, a little below the water-cock, and is also provided with a cock, which, working in concert with the other, serves to regulate the flow of gas. It is the end of this branch c d which is united to the copper tube m n by a joint-piece of India-rubber. Lastly, the lower end of the trompe opens into a cistern of water, which would in fact allow of measuring the gas drawn off by receiving it for a certain number of minutes under a glass receiver.

с

It might happen in many cases where the pressure of the gases in the main tube is strong that the trompe could be dispensed with, and the gas be taken, off at once into the

But in

It is a

lower cistern without using the current of water. any case it is more prudent to provide the trompe. simple means of regulating the flow of the gases. It may be made to come at the rate of three or four litres per minute.

Now, to collect a certain fraction of this gas-two or three litres in the course of several hours-it is only necessary to use the Mariotte vase above mentioned. For this purpose the tube m n is provided with a small tube h not far from its outer extremity. A bit of India-rubber tubing makes the communication with the straight tube of the Mariotte vase. The flow of mercury is regulated by a bent tube with cock, which may be raised or lowered at pleasure. And then a second upper tube of the Mariotte vase has also a tube with. a cock g, which is only used when the gas is drawn off for analysis. When the Mariotte vase has to be filled, the mercury must be let in by the vertical tube till it is full, and overflows by the cock g to expel all air. This cock is then closed, and the mercury rises to the top of the straight tube. Then by means of the India-rubber the connection between this straight tube and the tube h of the copper tube m n is made. If the gas does not come off spontaneously by the India-rubber, a slight aspiration must be applied so as to expel all air it may contain, and then make the joint with the straight tube of the Mariotte vase.

What has been said above is sufficient to explain the working of the apparatus. It appears that by a double system of aspiration specimens representing as exactly as possible the average of the gases flowing from the furnace during several hours may be taken for analysis. It will of course be well, should the tension at the moment of charging be very different from the general tension, to desist from

drawing off the gas until a certain interval has passed, until the usual régime is re-established.

As to the analysis of the gases thus collected nothing is more simple, as it is only required to determine the proporCO2 tions of It is not necessary to measure or weigh the CO gas which has to be examined. The way to operate is as follows: The gas comes out slowly by the cock g from the Mariotte's vase, by letting in mercury by the straight tube. The gases are dried in U tubes with chloride of calcium, or pumice stone with sulphuric acid. The carbonic acid is taken up by potash tubes. Burn the carbonic acid (CO) by the oxide of copper, retain the water formed by the small quantity of hydrogen present, and then determine the carbonic acid produced from the carbonic oxide by means of a second system of potash tubes. This analysis will only be inaccurate in cases where the gases contain appreciable quantities of carburetted hydrogen, which never takes place when the furnace is working with coke.

A last precaution is perhaps necessary in taking the specimens of gas. There are furnaces which smoke a good deal, or in which the gases carry off quantities of fine dust. In such cases the slit in the copper tube might get obstructed more or less. This happened to M. Scheurer-Kestner in his experiments when there was much smoke. This difficulty may be overcome as this able chemist did it. A little rake, composed of a short slip of copper put into the copper tube, could be drawn backwards and forwards by a rod passing on the outside, and thus the slit kept clear.

Having determined the ratio

CO2
CO'

the mean temperature

of the gases should be determined. When the mine is not. hydrated ores the temperature of the gases may rise to 400° or even 600° C., which renders the mercurial thermometer inapplicable, and there the thermo-electric pyrometer, or the resistance thermometer of Siemens, or the pyrometer of Lamy, based on the variable tensions of CO2 derived from the decomposition of the carbonates of lime and magnesia.*

§ 10. Determination of the caloric consumed in Blast Furnaces. -Suppose we have determined the two elements we have CO2

been considering =m, and the temperature of the gases

CO

as they leave the furnace.

Let us now see how we can employ these elements to determine the working of the furnace. The question is to compare exhaustively the caloric received and the caloric consumed. It has been already shown how the caloric generated in the furnace by combus. tion may be calculated, when we know the total weight of CO2 and CO in the escaping gases. Further on it will be shown how the caloric produced near the twyres-in the zone of fusion, and that generated in the zone of reduction, may be separately estimated. In both cases the caloric carried in by the hot blast must be added to the caloric produced in the furnace, in which there is no difficulty if we know the temperature of the blast. It is the sum of these two quantities, caloric produced and caloric thrown in, which makes the total quantity received. For the present, let us show how the caloric consumed may be determined.

It is composed of four parts:

1. The caloric absorbed by the reduction of the ores and

* Comptes Rendus, tome lxix. p. 347.