whereas the economical effect often involves other considerations, such as the maximum production of iron of a certain quality regardless of the maximum technical effect. In most cases, the iron-master is chiefly interested in the technical effect.

There is however one factor of technical effect, viz., that of the superheated blast, which has for the last three years excited the liveliest controversy.

The section 25 of the "Studies" treats of this question on the basis of the experience recorded by Mr. Bell and others in the Transactions of the Iron and Steel Institute, and on the assumption that the combustible for heating the blast is the gases of the furnace itself. M. Gruner's examination of the question is, like that of Mr. Bell, full of instructive applications. of the actual theory of the blast furnace. The complete technical answer awaits the result of experience of the cost of superheating the blast. To the question, whether there is advantage in heating the blast to 800°, 900°, or 1000°, the theoretical answer is undoubtedly Yes. For each rise in temperature of the blast there is increased economy, abstraction being made, of course, of the cost of maintaining and firing stoves for heating the blast. At the same time, this economy decreases rapidly with the rise in temperature. The economy arising from each accession of 100° to temperature of blast is much less from 800° upwards than from 500° to 700°, and still less than between 400 and 500°, and thus in practice it is useless to exceed 700° to 800°. Not having been able to collect sufficient data as to the cost of making and maintaining the stoves for superheating the blast, it

is impossible for me to add to the weight of this opinion of M. Gruner, excepting to say that, after examination of all the facts hitherto published, superheated blast beyond the limits safely reached by the cast-iron stoves is useless; and if, as seems to be the case, it be thought necessary to erect generators of gas to heat brick stoves, that system is certainly wasteful, and a retrograde step in blast-furnace engineering. This subject is again alluded to in Note V., Appendix.

Some apology is due for writing so much as an Appendix. The truth is, that I examined each subject and factor mentioned in the original text for myself, and conceived it might be useful to others to record my notes for their use.

TOTTERIDGE, September, 1873.

LEWIS D. B. GORDON.

STUDIES OF BLAST FURNACES.

§ 1. Recent modifications in the régime of blast furnaces.— For several years past the minds of metallurgists have been much preoccupied by two important modifications made in old Blast furnace practice. The furnaces have been increased in height and in diameter, and the blast is spontaneously heated to a red heat, in England especially, by means of large stoves of fire-brick, prepared by Messrs. Cowper-Siemens, and Mr. Whitwell.

Successive transformations in these two directions have resulted in what is deemed exaggeration by metallurgists, such as Mr. Lowthian Bell, whilst there are others who consider there is no limit save practical possibility. This divergence of opinions has been made known by the publications of the Iron and Steel Institute-an association frequented by Bessemer, Bell, Menelaus, Williams, Snelus, Parry, Siemens, Cochrane, and others well known as leading men in the iron industry of Britain. The question is one well. worthy of careful examination and study in reference to the chemical and calorific reactions which come into play in these enormous apparatus. I shall, for this purpose, make use of the series of highly interesting memoirs which Mr. Lowthian Bell has published in the Journal of the Iron and

Steel Institute,* and compare them with my own personal researches on the same subject, some of them given, for many years, in my course of lectures at the École des Mines of Paris, and others recently published in the Recueil des savants étrangers, and in the Annales de physique et de chimie.†

§ 2. Successive enlargements of blast furnaces.-Blast furnaces, working with charcoal as fuel, are seldom more than 30 to 35 feet high, nor have they more than 800 to 1200 cubic feet capacity. In Austria, in Russia, and in Sweden, where circumstances admit of a great accumulation of fuel, the height is carried to 45 feet, and the cubic contents to 1800 to 2200 feet. In coal districts the furnaces have been, from the beginning, made larger: and yet the ordinary furnaces of Staffordshire have not more than 2200 to 2500 cubic feet capacity, with a height of 38 to 42 feet; and even the largest do not exceed 3500 to 5000 cubic feet. In 1830, the capacity was not more than 2000 cubic feet as an average, and in Wales 2200 to 2500 cubic feet. In 1860, however, M. Lan and I found that there was a decided tendency to enlargement of the furnaces. In Scotland there were furnaces of 3000 cubic feet, and even 7000 cubic feet; and in Wales the furnaces were of 3000 and up to 5000, with some few as large as 7000 and 7750. These successive enlargements were made with the special object of increasing production, and we were convinced that, in fact, the yield had increased in proportion to the internal capacity.

In the enlarged as in the smaller furnaces in England, the yield was, on the average, a ton of Nos. 1 and 2 iron for 7 to

* Published in one volume complete, with Index, by Messrs. Routledge, in 1872.

↑ Savants étrangers, t. xxii.; Annales, etc., Mai 1872.

8 cubic metres (245 to 280 cubic feet) capacity, a ton of forge iron (gray) Nos. 3 and 4 for 210 to 245 cubic feet, and a ton of mottled forge pig for 175 to 210 cubic feet capacity.

By comparing together a great many Continental furnaces, I had previously arrived at the same results. In my lectures these figures were given as results to be used in determining the dimensions of blast furnaces.

In 1851, the first blast furnace was erected in Cleveland, by Messrs. Bolckow & Vaughan, who built it 42 feet high, and of 4500 cubic feet capacity.

In 1853, Messrs. Bell Brothers founded the Clarence Works, and erected several furnaces 48 feet high, and of 6200 cubic feet capacity.

From 1853 to 1860, a great many furnaces were erected in this district, but none of them were carried to a greater height than 58 feet, with a capacity of 7000 cubic feet, and the greater number were about 50 feet high, with 5200 to 6000 cubic feet capacity.

On the other hand, beginning from 1861, there took place a prodigious enlargement of the furnaces, of which we may give the following examples:

In 1861, Messrs. Whitwell & Co. built three furnaces at Thornaby 60 feet high, and 13,000 cubic feet capacity.

In 1862, Messrs. Bolckow & Vaughan carried the height to 75 feet, and the capacity to 12,000 cubic feet.

In 1864, Mr. Samuelson built his first furnace, at Newport, 68 feet high and 15,300 cubic feet capacity; and Mr. Thomas Vaughan carried the height to 78 feet, and the capacity to 15,750.

In 1866, Messrs. Bolckow & Vaughan adopted the lofty type of 96 feet, with only 15,000 cubic feet capacity; and