HIGHLY REFRACTORY CLAYS.

Clays which are sufficiently refractory to merit this classification are found chiefly in the Woodbridge clay bed, and mostly in the vicinity of Woodbridge. Two grades are dug, No. I fire clay and ball or ware clay, but not all the clays known by these trade terms can rightfully be called highly refractory.

Fire clays. At the middle or base of the section in many pits, there are often two grades of fire clay, known to the miners as the No. 1 and No. 2. The No. 1 is generally a fat, bluish clay, while the No. 2 is commonly mottled red and white, yellow and white, or sometimes bluish, but differing usually from No. 1 in being more sandy.

The character of the No. I fire clay found in the different pits varies somewhat, especially in point of refractoriness, as is shown by the detailed tests given below.

No. I fire clay is used in the manufacture of the best grades of fire brick, and there is consequently considerable demand for the material. Some of the No. I fire clays are also sold for saggers, the producers claiming to receive from $3.00 to $3.50 per ton for it. The supply of it is rather limited in the region around Woodbridge, and this is unfortunate, since it represents the most refractory type of clay found in Middlesex county, or even in New Jersey. As the Woodbridge fire-clay bed is followed to the southwestward it is found that the No. 1 clays drop off considerably in their fire-resisting qualities.

Detailed tests.—No. 1 fire clay, from pit of M. D. Valentine & Bros. Company (Loc. 14). This is a bluish clay (Lab. No. 382) with very little grit, even texture and smooth fracture, passing entirely through a 100-mesh sieve and slaking fairly fast. The air shrinkage was 7 per cent. when tempered with 25 per cent. of water, but the briquettes invariably cracked in drying, so that it was impossible to measure their tensile strength. The burning tests were as follows:

Burning tests of No. 1 fire clay. M. D. Valentine & Bros. Co., Woodbridge.

It showed many small cracks at cone 3, and burned steel-hard at cone 5.

When tested in the Deville furnace at cone 27 it was not beyond incipient fusion, and fused above cone 34. It is, therefore, a very refractory clay, but owing to its cracking, cannot be used alone. It has the following chemical composition:

Chemical analysis of No.1 fire clay. M. D. Valentine & Bros. Co., Woodbridge.

This clay is low in fluxing impurities and moderately low in silica, so that from the analysis alone its refractoriness is apparent. In order to show the percentages that would appear in the burned clay, the re-calculated analysis with the water omitted is given in the second column.

No. I fire clay, Anness & Potter.2 A second sample of No. I fire clay, from the pit of Anness & Potter (Loc. 6), resembled the preceding in its properties. It is a soft, grayish-white clay (Lab. No. 373), of irregular fracture and medium porosity, slaking slowly in water. The water necessary to work it up was 33 per cent., and gave a plastic mass averaging 41 pounds per square inch in tensile strength. The air shrinkage was 5 per cent. In burning the material behaved as follows:

Burning tests of No. 1 fire clay. Anness & Potter, Woodbridge.

1

This column gives the analysis re-calculated to 100 per cent., with the water left out, and shows the percentages as they would be after the clay is burned. No. 5 of section on page 455.

thickness of sand.

It burned steel-hard at cone 5 and warped but little. The material was barely incipiently fused at cone 27 and fused above cone 34. Its analysis was very similar to that of the preceding sample from locality 14, and was as follows:

Analysis of No. 1 fire clay. Anness & Potter, Woodbridge.

The percentage of titanium is slightly higher.

Refractory tests alone were made of some other samples with

the following results:

Fusion tests on highly refractory clays.

Locality.

Owner.

Material.

No. 9 Woodbridge, . Dixon Bank,

...........Buff clay,

do.

Fine fire clay,

Black fire clay,

No. 21
P. J. Ryan,
No. 90 Bonhamtown, J. Pfeiffer,

No. 61 Burt Creek,.. Sayre & Fisher Co., Clay from old Cream

Ridge bank, ....

No. 69 Sayreville, ... Whitehead Bros., . Sandy clay, Whitehead's

sandpit, .

Cone.

.33 vitrified. .34+viscous. .33+viscous."

.32 vitrified.

...33+viscous.

In respect to their refractoriness, all the above compare well with the best clays tested in this country,1 as can be seen from the following table: