proper size of hammer to be used on different classes of general blacksmith-work, although it will be understood that it is necessary to modify these to suit conditions, as has already been indicated.

Steam-hammers are usually operated at pressures varying from 75 to 100 pounds of steam per square inch, and may also be operated by compressed air at about the same pressures. It is cheaper, however, in the case of compressed air, to use pressures from 60 to 80 pounds instead of going higher.

In figuring on the boiler capacity for steam-hammers, there are several things to be considered, and it depends upon the number of hammers in use and the service required. It will vary from one boiler horse-power for each 100 pounds of falling weight up to three horse-power for the same weight, according to the service expected. In a shop where a number of steam-hammers are being used, it is usually safe to count on the lower boiler capacity given, as it is practically safe to say that all of the hammers are never in use at the same time. In a shop with a single hammer, on the other hand, and especially where hard service is expected, it is necessary to allow the larger boiler capacity, as there is no reserve to be drawn on, due to part of the hammers being idle, as in the other case.

Steam-hammers are always rated by the weight of the ram, and the attached parts, which include the piston and rod, nothing being added on account of the steam-pressure behind the piston. This makes it a little difficult to compare them with plain drop or tilting hammers, which are also rated in the same way.

Rules for Finding the Capacity of Steam-Hammers, and the Horse-Power Required for Operation

I call attention to some simple rules regarding steam-hammer practise, which may be of value to some of my readers. The first of these rules gives the horse-power required to run a hammer of any size, and may be expressed as follows: Divide the rated capacity of the hammer, in pounds, by 100, and the quotient will be the horse-power required to run the hammer constantly.

This rule is also applicable in cases where the hammer is not run constantly, by estimating the amount of time the hammer is idle each hour and making allowance therefor. But it will be noted that in case the hammer is not run constantly, or nearly so, and the horse-power is correspondingly reduced, sufficient steam-storage space must be provided in the boiler to prevent the steam-pressure being drawn down much faster than it is made during the working period.

The second rule deals with the estimate of the proper size of hammer to be used in working iron and steel of any desired cross-sectional area. The rule is as follows:

Multiply the greatest cross-section desired to be worked in the hammer by 80, if of steel, or, 60, if of iron, and the product will be the rated value of the hammer required in pounds.

This rule will give a hammer for safely working material of the size specified, at one heat. No doubt many of my readers are doing what we frequently do, that is, work billets which exceed in size that which would be allowable if the rule was always followed.

Development of Steam Drop-Hammers

Without raising the question of who was the pioneer in steam drop-hammers, Mr. F. B. Miles, who later became a member of the firm of Bement, Miles & Co., designed in 1872 what seems to be the first steam drop-hammer made by his company, and which was sold to the Baldwin Locomotive

Works.

Since that time this class of machinery has grown to be a large factor in the product of Bement, Miles & Co., now the Niles-Bement-Pond Company.

Since the first hammers were made by Mr. Miles, there has been little change in the important points of construction, such modifications as have been made being simply augmentation, with the vital or working parts as he conceived them. As a proof of the good design Mr. Miles produced, I have to point out that most, if not all, steam-hammers manufactured in this country to-day are constructed on the same lines, and the illustrations of them point very strongly to direct copies of what has become known throughout the trade as "Bement hammers," which shows a growth of the same mechanism produced over thirty years ago by practically the same company, and with no radical differences in principles.

CHAPTER VI

STEEL AND IRON: TWISTING, REDUCING, AND FORGING.
TREATMENT FOR WORKING IN MACHINE FORGING

Action of Steel and Iron Under Different Degrees of Heat

A FEW years ago some ornamental forgings were being made by students in the blacksmith-shop of the Alabama Polytechnic Institute. The designs included some pieces of 1⁄2 inch square, which were to be twisted, and the students were having difficulty in getting a uniform pitch to the twist. The iron would be heated for several inches, clamped in a vise, and twisted with a pair of tongs. As would naturally occur, the piece of iron was clamped in the vise and clasped by the tongs near the ends of the hot part where the heat merged from red to black. In almost every case when the twist would be made it would appear greater at the ends near the vise and tongs.

The first conclusion was that the fastenings must exert some influence to produce the effect. A piece was tried with the fastenings attached directly to the bright parts. In this case the twist came out very uniform. A long piece was then heated in the middle and clamped at the ends where the irons were cold. On making the twist the same effect was observed as at first, the greater twist occurring in the dark-red heat.

Samples of 1⁄2-inch round iron were then tried to see if the form of cross-section had any influence. So far as could be observed, the effect was the same as the square iron. The forge in which the specimens were heated was thoroughly cleaned and samples of 1⁄2-inch round iron were then tried to see if the form of cross-section had any influence. So far as could be observed, the effect was the same as the square iron. The forge in which the specimens were heated was thoroughly

cleaned and a fresh fire built with the good, clean blacksmith coal, samples of which were analyzed in the Chemical Laboratory and shown to be very low in sulfur and phosphorus. The results were the same as before.

Finally, two students-Messrs. J. S. Black and M. F. Kahm-took up the investigation as a subject for this work, spending a good deal of time and obtaining the following results. The work, while not exhaustive, covered a good deal of ground and was carefully done. The results are interesting if they establish, as the writer believes they do, that wrought iron is stronger when at a white heat than when at a red heat.

Careful search was made through the literature available, but only one reference was found alluding to similar observations. This was in the American Machinist of November 11, 1897, in an article by Mr. B. F. Spaulding. He says: "There is a peculiarity about some iron which I have often observed with curiosity, but which I do not remember to have seen mentioned. If a bar of this iron is heated for some distance in the length of it to a uniform white heat, it appears to be stiffer in that portion than it is at the lower temperature, the red-hot part, which intervenes between the cold ends and the white hot part.

"This peculiarity of being less readily bent where it is the hottest is shown when an attempt is made to bend it by letting the middle rest against something, as, for instance, the horn of the anvil, while each end is pressed in a direction to bend the bar. The bar will then have a greater bend at the places where it is red than along the part where it is white."

Materials Used in Experiments

The inference from reading this article is that Mr. Spaulding only attributed this property to certain kinds of iron, or to iron under certain conditions, but the experiments seemed to show that all wrought irons are similarly affected. The material for these experiments consisted of the following stock, all 1⁄2 inch square and ordered from a jobbing house: Jessop tool