State, they followed closely the English process and made their material quite wet before putting it in the form for the kiln, and Saylor, in his first Lehigh works, dealing with cement rock and argillaceous limestone as his raw material, tried first, as already stated, to make Portland cement by the mere calcination at high temperatures of the rocks, and, failing in this, he quickly went back and followed the English practice by grinding the materials dry and, after wetting and pugging, making them into bricks by hand. All the old methods of preparing the raw material are, as can be seen, predicted upon supplying to the flame of the kiln a property proportioned, thoroughly pulverized material sufficiently mixed, made into forms of some kind, duly dried and thereby presenting to the flame of the kiln a new rock or stone, containing all the ingredients in proper mechanical union for proper calcination. The more modern American methods, based upon the more modern American kiln, which has worked a revolution in the industry, works at a greater economic advantage in the handling of the raw materials. The marls and clays, but more especially the cement rocks and argillaceous limestones, are handled with the greatest economy and greatest dispatch, and while in the handling of marls which in themselves contain a great amount of water the process has been moderately successful only. In the Lehigh field of the State of Pennsylvania, where the great body of argillaceous limestone is used as above stated, this process, with material of this kind, has produced a wonderful development and by it the rock lying in quarries is brought in cars to the crushers and thence by elevators and conveyor to various forms of mills and ground into a powder. Thence, the material having been properly proportioned by chemical analysis is delivered into the kiln ready for calcination, without going into the expensive method of preparation under the old processes first described. Broadly speaking, therefore, it may be stated that the object of the preparation of the material for the kiln, is to have it as intimately mixed as possible, so as to form a homogenous substance, whether in bricks, balls or other shapes or in powder of infinite fineness.

Kilns. The form of kiln originally used in England and Germany and largely used there at the present day, is the "bottle," or dome kiln, where the raw material above referred to in bricks or other shapes is charged between layers of coke. The kiln is unloaded at the bottom and after the material is drawn from the kiln in the form of clinker the over-burned and under-burned material having been picked out, it is ready for the next operation of grinding.

The books are full of the many variations of this "bottle" kiln and the utilization of the heat in the drying of the raw material. As

it is drawn and charged, and a greater amount of heat is lost while the calcination is going on, and for the purpose of economy in this direction, drying chambers of various kinds have been used, and various forms of construction have been adopted.

Other forms of kiln are also used, one of the most important being the "Hoffman," which consists of a series of chambers built around a central stack, and my means of dampers the gases of the burning chambers are utilized for the drying of material which is placed in the chambers forming a part of this continuous group. Various adaptations of this kiln are also to be seen in Belgium and Germany. The "Hoffman" kiln enabled the manufacturer to use coal, where as coke had been practically the only fuel economically and successfully used in the old-fashioned dome kiln. In order, therefore, to still further utilize coal and make greater economies, the German set out to devise the adoption of the continuous dome kiln to the manufacture of Portland cement. The Shoefer, the Dietsch and the Schneider kilns are forms of what is known as the Etagen kiln, or kiln in several floors, the first two being of great heighth have a drying chamber above, a fire zone half way down and a long cooling chamber beneath. The material for these kilns is brought up by elevators, and after calcination, the clinker is taken out below. The Schneider kiln is more especially adapted to the rejuvenating of the old dome kilns, increasing their output at moderate expense, making them continuous.

In France, the Bauchere and Candlot kilns are forms of the German continuous kilns, but instead of having high stacks, they have draught flues from a group of kilns connected with a single stack, which form drying chambers and heating surfaces for the drying of the raw material. All these forms of kilns are applied only to the calcination of the cement making material, when presented in the form of brick or balls or other definite shapes, because if the material were placed in powder, the choking of the kiln would promptly ensue. They are all based upon the European method of handling the raw material. A more economical method of handling the raw material grew out of what is known especially as the American revolving kiln.

The American Revolving Kiln.

Strange to say, this kiln had its origin in Europe, and was the invention of Ransome, who was a cement expert and the originator of the well-known Ransome concrete construction. It proved a failure in England and its early days in this country were also marked by adversity. Subsequently, under the successful direction of Navarro, Giron and Whittaker, it was perfected, and in it by

it and the economies it has permitted, is due the wonderful growth of the industry in this country. This kiln, which is shown in the accompanying cut, is an iron cylinder of about sixty feet long by six feet in diameter, and revolving at about one revolution per minute. At one end the raw material is introduced and at the other a

flame produced, either by the injection of oil or by driving in by forced draught of pulverized coal is admitted. The effect of the fire is first to drive the moisture and carbonic acid gas out of the raw materials, and subsequently to calcine it into a clinker in the shape of small lumps or nodules. This clinker produced, drops out at the lower end of the kiln, is conveyed to a cooler, a high iron tower, with forced draught, where it is subjected to the action of the

Crushing and Grinding Machinery.-When under the American process it became possible to make cement from practically dry material, as is the case with more than three-fourths of all that is produced in this country, a great economy was effected, both in the fuel consumption and in the handling of the material before calcinaation. To drive out the moisture from the wet material, in some cases 50 to 60 per cent. of its total weight, a very large proportion of heat had to be used and nearly one-half of the fuel consumed was for the purpose of expelling this water, either added to or found combined in the raw material. It is needless to say that this water added also the bulk of the raw material, and required handling at all the stages of the process, up to and including the process of calcination.

To dispense with this costly process, which could be done by the use of dry raw material, naturally required heavy crushing and grinding apparatus to handle the raw rocks, which took the place of the wet clays, marls and chalks. The American manufacturer was ready to grasp the mechanical appliances invented for this purpose and used in this country. The "Gates Crushers," see