By a process of refining, a bitumen of about the consistency of maltha is produced when required. It is first separated from the sand by being boiled in water. The bitumen, having a less specific gravity than the water, rises to the surface, when it is skimmed off, and the operation continued as long as desired.

Montana Asphalt.

A deposit of bitumen generally termed asphalt, but not strictly so under the definition previously given in this chapter, is found in Montana. At ordinary temperatures it is soft and will pour slowly. Upon being treated with carbon bisulphide, 95 per cent was dissolved. Treated with gasolene 80 per cent was found to be petrolene, the insoluble matter in both cases being leaves, feathers, bugs, flies and other insects. The deposit has never been developed commercially.

Cuban Asphalt.

There are four distinct submarine deposits of asphalt situated in the Bay of Cardenas, all within twenty miles of the city of the

same name.

The first is in the western part of the bay and is practically pure bitumen. It is used principally in the manufacture of varnishes. It has been mined here since about 1870 by sinking a shaft some 125 feet deep in the bottom of the bay. The operation of mining is very simple. A lighter is moved over the shaft and a long iron bar, pointed at the end, is dropped so that its own weight detaches portions of the asphalt with which it comes in contact. The operation is repeated until a sufficient quantity has been detached, when a diver loads it into nets and it is hoisted to the surface.

The other deposits produce a lower grade of material which is suitable for pavements. They are operated in practically the same manner as that just described. The largest of these is about 15 miles from the city, near Diana Cay. It has been operated since 1870, producing some 1000 tons per year without any apparent diminution in the supply. This deposit seems to be inclosed within a circumference of about 150 feet and in water 12 feet deep.

There are also deposits of asphalt near Puerto Padre on the north coast of the island, as well as some liquid bitumen near Santiago de Cuba.

Barbadoes Asphalt.

A variety of bitumen known as "glance pitch" has been known for some time on the island of Barbadoes. It is a hard brittle asphalt, breaking with a clear brilliant fracture. It occurs in veins from an inch to a foot in thickness. It has never been used in, and is not suitable for, pavements, but its output is entirely consumed in the manufacture of varnishes, etc. It is almost wholly soluble in carbon bisulphide.

Asphalt in Turkey.

An important asphalt mine is located near Avalona on the Adriatic Sea. It belongs to the Sultan, but has been leased to a French syndicate. The material is taken out in both a solid and a liquid state and is exported to Europe and America. There are also other mines in the interior of Turkey in Asia belonging to the government and private parties, but they have not been worked to any extent on account of the bad transportation facilities.

Dead Sea Asphalt.

About the Dead Sea there is quite a quantity of asphalt belonging to the government. It is not used for any purpose, and persons found collecting it are fined or otherwise punished. It is said that in former times asphalt was frequently found floating on the surface of the Dead Sea, especially after earthquakes.

Syrian Asphalt.

There are four asphalt mines in Syria, but the one at Hasbaya is the most important. The mine has been worked at intervals by different lessees since 1864, but only 1000 tons per annum were taken out when actual operations were carried on. It is the private property of the Sultan, and has not been worked to any extent since 1893. From 1882 to 1892 about $70,000 worth of this material was exported to the United States, and in 1897 $3439 worth. In 1893 the product was worth about $90 per ton.

It is said that asphalt exists in this vicinity in large quantities, and under a favorable government thousands of tons might be mined each year.

A sample of the Hasbaya product is thus described: It is black with a bright jetlike lustre, making a blackish-brown streak on unsized paper. It is so brittle that pieces may easily be broken off with the fingers. It is very combustible, but a splinter held in the flames will melt before igniting. Its specific gravity is 1.104.

Egyptian Asphalt.

No natural asphalt is found in Egypt except in very small quantities above Suakim near Abyssinia, where it cannot be worked profitably, and some small deposits on the east coast of the Red Sea.

It is said, however, that two firms in Egypt manufacture artificial asphalt, importing material for their use from Italy, France, and England. What their process was, or to what uses their product was put, could not be learned.

CHAPTER IV.

BRICK-CLAYS AND THE MANUFACTURE OF PAVING-BRICK.

THE word clay as ordinarily used means any earthy substance which can be worked up with water into a plastic mass that when dried will retain any shape into which it may have been formed. Strictly speaking, the term applies to a single mineral, hydrated silicate of alumina, or kaolin. It is not, however, a natural mineral, but is the product of the decomposition of feldspar.

Beds of feldspar have often been found covered by the kaolin formed by the decomposition of a portion of its mass. This occurs when the feldspar is exposed to the action of water containing carbonic acid gas, which acts upon the alkaline base of the mineral and carries it away in solution, leaving the silicate of alumina behind. As, however, feldspar is seldom found in large quantities by itself, so deposits of pure kaolin are very rarely found. Commercially they are of considerable value.

When pure, kaolin is composed of:

3

This is represented chemically by the formula A120,2SiO2H2O. It is the base of all the substances known as clays, and as they are formed by the decomposition of rocks, so their chemical composition varies with that of the rocks from which they are derived.

Quartz and feldspar are the two minerals found in the greatest abundance in the earth's crust, and, very naturally, it is expected to find sand and clay as the most common of the products of the decomposition of rocks.

Feldspars are divided into three separate varieties: orthoclase, or potash feldspar; albite, or soda feldspar; and anorthite, or lime feldspar, each of these varieties being minerals more or less complex. These, too, are at all times in the same mineral, which must be named by one of the terms used in the classification, the one in greatest abundance giving the character to the compound.

All feldspars are acted upon by the atmosphere. The oxygen, carbonic acid, and water contained in it, when taken together, form a solvent that is hard for rocks to resist, especially when supplemented by soil-waters containing more or less acids derived from decaying vegetable products.

Under these influences granites and other rocks containing feldspar, especially the potash variety, are rapidly decomposed. The feldspar having lost its cementing property, the rock falls into pieces. The carbonate of potash is dissolved in the water and borne away. The particles of quartz, mica, and other accessory minerals remain and become assimilated with silicate of alumina from the feldspar, all together making up the product commonly called clay. It can be readily seen that it cannot be a pure mineral and that its composition must vary greatly.

Kaolin has a specific gravity of from 1.5 to 2.2 and is white in color. It is soft to the touch when dry, and very plastic when wet. It has two marked chemical characteristics, insolubility and infusibility. It being the product of a soluble body, the former might be expected. It is not affected by ordinary chemical agents, nor by temperatures that have thus far been produced in the arts. It is consequently of greatest value in the manufacture of crucibles and other refractory utensils used in chemical research.

While this infusibility is true of kaolin, it is not true of clay. For the addition of different minerals found in nature often forms a compound that is easily fused. These minerals when thus used are called fluxes. Naming them in the order of their effectiveness, they are potash, soda, iron, lime, and magnesia. Very small amounts of one or more of these substances are required in any clay to destroy its value as a refractory material.

But on the other hand the finely divided silica of the original rock which is always found in a greater or less amount in most kaolin detracts not at all from its heat-resisting qualities, the silica