Soda is one of the compounds found in most clays. Alone, or in combination with potash, it exerts a fluxing action on burning clay. In kaolins it ought never to exceed 3 per cent., or 7 per cent., soda and potash combined. In fire clays the two alkalies (soda and potash) should not have a maximum of more than 5 per cent., better at 2.5 per cent. to 4 per cent.;-but in paving brick or ordinary brick the two may run as high as 15.50 per cent.

Potash is another compound which may be found in clay. When clays contain as much as 35 per cent. potash-feldspar, it may be safely concluded that there is about 5 per cent. potash. The permissible limit of potash in fire clay is 4 to 5 per cent., depending on the physical properties of the clay; while in paving brick the total of soda and potash combined may be as high as stated. The usual average of potash and soda combined as alkalies in Pennsylvania clays is from 1 to 3 per cent. In practical use the alkalies in kaolins, for highest quality of product, should not exceed 1 per cent.; in fire clays 1.50 per cent.; in pottery clays, 2 per cent.; and in brick clays, 2.65 per cent. An excess of potash-feldspar added to a white burning clay produces a creamy tint when burned. Potash deepens the color of ferruginous clay when burned.

Phosphorus in the form of phosphoric acid is also known to occur in some Pennsylvania clays, especially near iron ores. Generally the quantity is too small to have any marked deleterious effect; but, in a thorough analytical search, it ought to be included, particularly if the other combined constituents are less than 100 per cent.

Sulphur, if it occurs at all, is generally in such minute quantity that its effects need not be considered here, except in combination with magnesia, as heretofore stated.

Titanium is another element that is very common in Pennsylvania clays. For many years in analytical work on clays no attention seemed to be paid to it. In some of the clays of this State as much as 5 per cent. titanic oxide has been found. Careful experiments show that it has a tendency to give a bluish color to stone and other ware, the larger the percentage, the more pronounced the color. When iron and titanium are both in clays, with an unusually high percentage of each, there is a tendency toward a dirty looking bluish black or greenish black color, depending upon the degree of temperature of the fire.

A small percentage of copper in the clays will also color the product a blackish green to a very dark blackish green.

The older clays of Pennsylvania some times contain small fractions of zirconia. If the clays also contain more than 2 per cent soda to not more than of 1 per cent. zirconium oxide, a light yellowish color will be given to the burned mass, graduating to an orange color as the percentages of the two elements increase.

A very small percentage of tungsten has also been revealed by complete quantitative analysis of some of the oldest Pennsylvania clays. If in the mass to the extent of of 1 per cent., and more than 3 per cent. soda, it will have a tendency to give a bluish green cast to brick burned at the usual temperature.

Magnetite occurs, if at all, in such small fractions that, as a general rule, it need not be taken into consideration.

There are other elements entering into Pennsylvania clays,―as, of the alkalies, the element lithia; also, ammonia; but the first is so rare, or the percentage thereof so small, that it need not be considered. The same may be said of ammonia, as it passes off as a vapor in the early burning stages. Chromium now and then occurs in southern Chester, southern Delaware, and southern Lancaster counties, but in such infinitesimally small quantities as to have little or no effect on the clay product.

Vanadium may also be found, which will show on the surface a green discoloration. This, if rubbed off, will appear again as long as the salt remains in the mass.

The elements entering into Pennsylvania clays have been considered in detail, on account of dissatisfaction at times relative to the output of promising clay beds. Before such beds are developed, the first wise step would be to have the bed or deposit carefully sampled, and the samples analyzed for all the constituents or elements mentioned above as of importance in the clay industry. Then steps should be taken to ascertain beyond peradventure the extent of the deposit or bed. Otherwise, serious loss may be entailed, by the erection of a plant, from an insufficient amount of crude material.

BURNING OF CLAYS.

In burning, much could be said about the proper temperature; but this will have to be taken up at length in a more extended report hereafter. Common bricks may not require a temperature of more than 1,850 degrees Fahrenheit; while other mixtures may call for 2,300 to 2,500 degrees Fahrenheit. The approximate temperature may be learned by the use of what is known as the Seger cones, two or more being placed in a kiln where they can be watched through a peep hole, at the same time not receiving the direct touch of the flame.

SHALE DEPOSITS.

Much of the stratified rock of Pennsylvania is commonly known. as shale. These shale deposits were once the sedimentary clays, that became hard by pressure. Many of them were afterwards uptilted, and are now found in various positions. When ground up,

and mixed with water, a mass is produced similar to common clays. Sometimes it is plastic, and sometimes non-plastic. When placed in water, unground, shales do not usually fall to pieces as ordinary clay does. They may be highly refractory (requiring an extraor dinary degree of heat to fuse), or extremely fusible (baked at a low temperature); but in either form they are commercially valuable, and much sought for in recent years for the manufacture of paving bricks. Some of the most refractory shales of Pennsylvania are being used in fire brick manufacture. Shale rocks form an enormous series of deposits in the northern tier of counties of this State; and these beds are numerous also farther south; and such have been operated successfully and profitably in some of the southern tier of counties, as in Adams. The Devonian shales seem to be best for vitrified bricks; the Salina shales make a good strong building brick, while the Medina make good pressed brick. Chemung shales, of the Devonian age, can be profitably operated for vitrified bricks in 35 counties of this Commonwealth, as follows: Bedford, Blair, Bradford, Cameron, Carbon, Centre, Clinton, Columbia, Crawford, Dauphin, Erie, Franklin, Fulton, Huntingdon, Juniata, Lebanon, Luzene, Lycoming, McKean, Mifflin, Monroe, Montour, Northumberland, Perry, Pike, Potter, Schuylkill, Snyder, Somerset, Sullivan, Susquehanna, Tioga, Union, Warren and Wyoming. A sample of shale rock gave the following results: Silica, 63.11 per cent.; alumina, 23.11 per cent.; iron oxide, 1.79 per cent.; lime, 0.42 per cent.; magnesia, 0.70 per cent.; alkalies (potash and soda), 3.71 per cent.; moisture, 7.05 per cent.; total, 99.89 per cent.

Shales of the Upper and Lower Silurian ages are abundant in this Commonwealth, though few of even the outcroppings have been touched for brick making purposes. One of the most successful plants, operating in these ages of shales, is located in the southern part of Cumberland county, where a large industry has been established, and the product shipped to the eastern cities. The Upper or Lower Silurian shales occur in the following counties: Bedford, Berks, Blair, Carbon, Centre, Clinton, Columbia, Cumberland, Dauphin, Franklin, Fulton, Huntingdon, Juniata, Lebanon, Lehigh, Lycoming, Mifflin, Monroe, Motour, Northampton, Northumberland, Perry, Schuylkill, Snyder, Union and York, 26.

In addition to those mentioned, we have large areas underlaid with Mauch Chunk red shale, Hamilton shale, Clinton shale, and Hudson river shale, all results of sedimentary clay deposits.

DELAWARE RIVER VALLEY CLAYS.

Returning for a moment to notable clays in Pennsylvania, mammoth beds of good brick material are found under the Delaware river mud in Bucks, Deleware, Montgomery and Philadelphia coun

ties. Independent of these deposits the abundance and excellence of the Delaware valley clay has made celebrated the Philadelphia house brick. The beautiful red color of the brick, due to a constant particular percentage of iron in the clay, contrasts strongly, as Prof. J. P. Lesley, former State Geologist, says, with the yellow bricks manufactured from the drift clay in other parts of America.

In summing up, it must not be forgotten that organic matter in clays affects the color as well as the plasticity, and also weakens the tensile strength. It affects the absorptive power as well. Most of these deterrents can be overcome by not heating the clay too rapidly for any purpose.

There are two other minerals which can be properly classified under the clays of Pennsylvania, viz: fullers' earth and slip clays.

FULLERS' EARTH.

Properly speaking, fullers' earth is not a clay, because it lacks plasticity; but, as Dr. Henrich Ries, of Ithaca, New York, has aptly said, in his report on the clays of New York, some of the material which is put on the market under this name, and does the work required of it as well as true fullers' earth, is ordinary plastic clay. Until the discovery of large bodies of fullers' earth in Florida, nearly all of this mineral used in the United States was imported from England. Now the southern product has come into general use. In Pennsylvania clays approaching fullers' earth in all its meritorious properties have been found in Centre, Lackawanna and Luzerne counties; but thus far no systematic plan has been adopted whereby to place the product upon the market. Fullers' earth was first used for fulling woolen cloth,—that is, cleansing it of its grease, but it is now extensively used for bleaching cotton seed oil, and for clarifying petroleum. There may be large deposits of this important earth in this State. In appearance it resembles clay; but in its properties it differs considerably, as it usually lacks plasticity, and also has the power of absorbing large quantities of greasy substances. When analyzed, it shows very little difference from ordinary clay, except that it is unusually high in combined water. It adheres strongly to the tongue, when tested in this manner; but some of our ordinary clays have the same property. The only reliable way of ascertaining whether a sample is fullers' earth or not, is by an actual test in the laboratory. Recently fullers' earth has had application in the manufacture of certain soaps made for removing grease and printers' ink stains.

SLIP CLAYS.

Slip clays are very impure and easily fusible clays. They are used for glazing stoneware, first being mixed with water to the consistency of cream, and the slip put on the ware by a brush. Some

times the ware, before burning, is dipped into this slip mixture. To be of commercial value it is required that it shall fuse at a low temperature to form a glaze of a uniform color, and a glaze that will not crack or craze. Thus far, notwithstanding any claims that have been made, it has not appeared native in Pennsylvania in any considerable quantity. The main supply is now derived from New York and Missouri. Some of it is obtained from Michigan, some

from Ohio, and some from Texas.

SAND LIME BRICK.

An important brick industry has been sprung up in Pennsylvania within the past five years,-the manufacture of artificial sand stone of sand lime brick. In some localities bricks thus made are finding favor with architects and builders, as well as the general public. The brick is made on the principle that a moist mixture of slaked lime and sand becomes hard on being exposed to air. Thus sand bricks are made with a lime silicate bond. In the manufacture treatment has to be made to suit the physical and chemical properties of the sand. On the other hand, full attention must be given to the kind of lime used. Some of the manufacturers expose the bricks after moulding, to the air for from 2 to 4 or 5 weeks before permitting them to be used in buildings. Analyses are made of the product after 8 hours' exposure in a steam cylinder, with a steam pressure in the atmosphere of from 120 to 150 pounds, maintained from 8 to 14 hours. Before using, the sand has to pass through a 20 mesh,-400 apertures to a square inch. Sharp sand is preferred, an a very high percentage of silica is essential.

Composition of the mixtures, two parts coarse sand-20 meshone part fine sand,-much finer than 20 mesh. When these parts have been thoroughly mixed, 10 per cent quick lime (CaO) is added. Then the mass is moulded into brick forms, 120 to 150 pounds per square inch steam pressure applied, the temperature of the hardening cylinder being about 185 degrees Centigrade; and the bricks exposed to the steam from 8 to 14 hours. The moulding pressure applied is 15,000 pounds per square inch.

The claim is made that by this process, with pure lime (CaO), the tensile strength, taken immediately after hardening, will be over 400 pounds, and the crushing strength over 7,700 pounds; that after freezing the tensile strength will be over 370 pounds, and the crushing strength over 9,000 pounds. Percentage of water absorption not over 8.60.

When dolomitic limestone is used instead of the high grade calcium oxide stone, the tensile strength is considerably less, and also the crushing strength, while the percentage of water absorption may be of 1 per cent. more. Some makers claim that the sand is