ON THE CHEMICAL MANUFACTURES OF THE NORTHERN DISTRICTS. 713 
and the colouring matters are skimmed off the surface of the liquor. The 
boiling is then moderated, and during the whole operation a stream of acid 
is supplied to the cistern. The sulphate of ammonia salts out, and is fished 
up into baskets to drain, when it is ready for the market. 
Cement.—The manufacture of this material on a large scale in this district 
is of comparatively recent origin. A small quantity of cement has long been 
made on the Yorkshire coast, near Whitby, where a peculiar mineral is found 
in the alum-shale, called the ‘‘cement stone.”? This mineral has been 
analyzed by Dr. Richardson, who found it to contain— 
Vay msolublein ‘acids’ Fs... Ve, See 18-41 
Consisting of silica ............ 12°24 
3 of alumina 5.7) S28, : 6°17 
Alumina soluble in acids ’............... 6:89 
sie OF iron.) , . PY eee eae 0-54 
NC ee eee ct ee ee, 37°68 
BRae nesta! cs J. :'. Sree cee 5°20 
moun nad potash .)... |; .. ste see ine traces 
Oeeanie matters... . J). .yieee es eee oe 1:45 
Carbonic acid and water ...........2.... 29°62 
99:79 
About 20 ewt. of this mineral is found in every 60 tons of shale, and the 
greater proportion is sent to Hull, where it is manufactured into a cement, 
sold under the name of Mulgrave cement. 
The mineral is burnt in small open kilns, and afterwards ground to a fine 
powder. 
The production of cement on a large manufacturing scale dates from the 
establishment of the works of Messrs. T. C. Johnson and Co., in 1856. This 
firm manufactures Portland cement, Roman cement, Keene’s marble cement, 
and plaster of Paris ; and they have recently introduced improved machinery 
for the more perfect levigation of the raw materials, by which the subsequent 
chemical action is much facilitated. 
Portland cement is very extensively used in this country, in France and 
Germany, for dock works, basins, fortifications, and for fronting houses in 
imitation of stone. It is also used for coating the inside of all first-class 
iron ships. The rivets are carefully coated, and are thus protected from the 
corrosive action of the bilge-water. It has been found of equal service in 
sugar-carrying vessels, where the leakage of the molasses exercises a very 
corroding action. 
Roman cement is prepared by calcining Septaria in open kilns, and after- 
wards grinding the burnt material in horizontal stoves. It is used either 
alone or mixed with an equal volume of sharp sand. 
Keene’s marble cement is made by soaking calcined gypsum in a solution 
of alum, and then recalcining the mass at a dull red heat. This recalcined 
material is then ground and sifted. It is only used for internal work, such 
as floors, skirtings, walls, &c. It is largely employed in London in churches 
and club-houses ; it rapidly dries after being applied, and may be papered or 
painted in two days. When dry, it is so hard that a nail cannot be driven 
into it. Two qualities are made, one of which can be polished in imitation 
of marble, while the other is used as a ground for painting: when different 
colours are introduced, a superior scagliola is formed. 
