In the manufacture of glass it is essential that the silex should be perfectly pure, as the slightest mineral taint affects the color.
At first the New England factories got their sand from Demerara, brought as ballast, and the quality was good. During the War of 1812 this source of supply was cut off, but Plymouth beach provided for the wants of the manufacturers, until a better sand was discovered at Morris River, N.J., though not up to the full requirement of the art. For ten years past, Berkshire County. Mass., has furnished sand; the best quality is owned by G. W. Gordon, Esq. By thorough washing, and passing it through fine sieves, and proper packing, he now commands the market, and delivers it ready for use. The purity has been tested, as shown by the following extract from a report by Professor A. A. Hayes, M.D., of Boston, Massachusetts State Assayer, of the result of analyses of three samples of Berkshire sand, taken from three different locations owned by Mr. Gordon, viz.:—
"For the manufacture of glass, the slight amount of earth, in mica and tourmaline, contained in these samples, is of no account, the impurity being such oxides as color glass. The analyses therefore give only the proportion of coloring oxides; and, for simplicity of statement, the total weight of coloring oxide in each sample is determined in one part or pound.
| "Sample B analyses: | 4000 parts of this sample contain one part of oxide of iron. |
| Sample C analyses: | 3333 parts of this sample contain one part of oxide of iron. |
| Sample P analyses: | 3460 parts of this sample contain one part of oxide of iron. |
"Sample B is equal in purity to the best sand known as a material for glass, in this or any other country."
FURNACES.
Next to pots, furnaces are most important for the success of a glass manufactory. Long ago it was seen that the old English plan was defective. They consumed coal at an extravagant rate, though this was not a serious drawback in England, because the furnaces were located near coal-mines, and run with a quality called slack, not otherwise merchantable. English furnaces were constructed with reference to durability, usually eight feet in diameter at the interior base, and six feet clear at the crown. This rule was followed in this country until 1840. The writer, having occasion to build an extra furnace, adopted the novel plan of one fourteen feet diameter at the base in the clear and only five feet at the crown, braced by binders, with cross-ties to prevent lateral expansion, which was a success.
A furnace on the old plan consumed 2575 bushels of coal weekly, and refined only 38,000 pounds of raw material. The new refined 35,000 pounds, with a consumption of only 2000 bushels of coal. Since then a further decrease in consumption of coal has been produced by the use of the Delano patent, which feeds the furnace by forcing up the coal at the bottom of the burning mass, thus consuming the entire smoke, and obviating the necessity of wheeling coal on the glass-house floor and impeding the workmen. It also does away with all danger to the pots in feeding the fires. Besides these great advantages, it distributes a regular and uniform heat to each pot, causing the pots to last much longer, and fusing the metal better,—important items to mixers.
From three to five tons of fuel is the weekly saving in a first-class furnace.
It is of vital importance to obtain pots that will last a reasonable time. Clays of the finest quality are essential. Each piece must be freed from any foreign matter, particularly sulphate of iron, which often occurs. The burnt and raw clay should be well mixed, wet, and frequently kneaded, or trod over by the naked feet. Tenacity must be secured, sufficient that a roll twelve to eighteen inches long can be suspended, and hold firmly together by its own adhesiveness. The next point is to make the pots free from air blisters, all portions being compact; then to dry them thoroughly, which requires great care on account of the inequality of the different parts. Pot-makers are not agreed as to the value of different clays, and the use and proportion of raw to burnt shells. Some use sixteen parts raw to eleven burnt, some fifty-five raw to forty-five burnt, some equal proportions of each.