allowances being made, scarcely as good results as those obtained in the coke furnaces of Great Britain, yet there are in the list some remarkable examples which lead to a contrary conclusion. Some of these have been given at 274 and following pages, from which it will be perceived that in certain cases there is an extraordinary proportion of carbonic acid1 as compared with carbonic oxide.

In order to compare the available heat developed per unit of charcoal with that produced from each unit of coke, the following estimates have been compiled :

On referring to the estimates of the quantities of heat available, as produced in coke and charcoal furnaces respectively it will be seen that, at first sight, there is a very close correspondence, in this respect, between the two. Taking C, D and E, given page 244, as fair examples of the former, we have :

:

The samples of gas were not taken in the manner now practised in the Clarence laboratory, viz. over a period of a couple of hours, but over very short periods only. Professor Akerman, in a private letter, expresses his belief in their general correctness, and points out that the quantity of fuel consumed corroborates this view. In this I entirely agree; because, if the weight of charcoal for a given quantity of pig is truly stated, the quantity burnt to the state of carbonic acid is necessary, in order to provide the quantity of heat required for the operation.

In like manner we may take a, e, f as illustrating the best examples of the charcoal process:

Practically coke, as supplied by the Durham collieries, may be considered dry, while the samples of charcoal chosen for illustration contained 9 per cent. of moisture. With this allowance the two sets of figures stand thus:

Viewed in this way, charcoal as burnt affords about 8.5 per cent. more available heat than is obtained from Durham coke of fair quality. There is however no proof whatever that the heating power of vegetable exceeds that of mineral carbon; but there does appear ample reason, accepting the correctness of the quantities of charcoal stated to be consumed in these examples, and of the analysis of the gases as representing an average composition, for believing that the circumstances attending the combustion of charcoal differ from those of coke.

There is not any material discrepancy in the loss by the escaping gases between the two kinds of fuel-nothing beyond what might be expected from the fact that charcoal contains so much water, the presence of which must necessarily cause considerable cooling of the volatile substances as they leave the furnace. The great difference in the calorific power, as between coke and charcoal, arises, as has been already intimated, from the high ratio of carbonic acid in relation to

carbonic oxide, which is generally found to prevail, when using charcoal. In consequence of this it appears, although the same numbers have been applied in estimating the calories developed by both kinds of fuel, that one unit of charcoal taken as dry affords by its combustion with air at 0° C. (32° F.), fully 9 per cent. more heat than coke, viz. 4,373 calories instead of 3,497.

Having regard to the high price of charcoal, it is somewhat remarkable that more has not been done in raising the temperature of the blast. On referring to the list of the Swedish furnaces, pp. 276 and 277, it will be noticed that for grey forge iron, in one instance, it is as low as 80° C. (176° F.) and that the average is only 184° C. (363° F.) In making Bessemer iron the highest blast heat is 300° C. (572° F.) and the average 273.7° C. (524° F.) It is true that in most cases all the escaping gases are utilized either in heating the air or in calcining the ore-the blowing power being usually water-so that there is usually no gas to spare. On the other hand, notwithstanding the loss of heat in all special air heating arrangements, yet a much less expensive fuel than charcoal can be used for the purpose; and therefore it seems strange that more attention is not paid to so important a question as that referred to. These observations have particular application to the fact that in the coke furnaces (in the examples given at page 281) for each unit of fuel burnt there are 671 calories due to the blast against 292 per unit of dry charcoal.

In seeking to secure any great economy of charcoal by increasing the temperature of the blast, it is necessary to consider the difficulties which have to be encountered. In the instance given of the Vordernberg furnace, the charcoal consumed is 12.60 units per 20 of iron. The weight of the blast is about 46 units, having a temperature of 450° C., and containing therefore 4,770 calories. Now this exceeds considerably the value of one unit of the fuel, in the state in which it is delivered to this Vordernberg furnace when it only gave 4,111 calories. If we so reduced the consumption of charcoal as only to need 40 units of blast, and heated that blast to 1,000° C. (1,832° F.), the heat it would contain would be represented by 9,480 calories or say 4,710 more than when the air had a temperature of 450° C. Now 4,710 calories is equal to about (119) 1·14 units of charcoal; which

represents the utmost economy to be obtained by raising the temperature of the blast to the probably unattainable temperature of 1,000° C.

It may be remarked that any decrease in the quantity of vegetable fuel is not, as in the case of coke, attended with any material decrease in the weight of limestone, the earthy impurity in charcoal being basic in its nature and insignificant in point of amount.

The arguments employed up to this time, to prove that charcoal as used in timber-growing countries does not differ materially, in point of quantity required for a given amount of work, from coke as used in England, have been chiefly founded on the experience of furnaces making rich pig iron for the converter. Before leaving the subject, it may be expedient to say a few words on the practice of charcoal furnaces when making white iron. For this purpose, the two Vordernberg furnaces Nos. 2 and 3, described in great detail by M. Friderici, are selected; the former of these is stated, page 274, to be producing a ton of pig with 14:80 and the latter with 12.60 cwts. of charcoal.1

The heat equivalent of one unit of dry charcoal compared with coke and calculated in the manner adopted, page 279 (i.e. allowing it as stated by Mr. Friderici to contain 7 per cent. of water), stands thus:

All perhaps that need be said as to these two instances of charcoal working, is that the high state of oxidation of the carbon is still more conspicuous than in the production of Bessemer iron; while the extent to which the general fund of heat has been aided by the heat in the blast is also somewhat higher-viz. 339 calories instead of 211, which latter is the average of the Sandviken, Bangbro, and Guldsmetshyttan furnaces, reckoned upon charcoal in its dry state.

Experience with modern Cleveland furnaces in the manufacture

There are some grounds, for supposing that this (12.60) may be understated.