Our gardens, fire engines, brewers, and pump-makers (for suction, &c.,) have found the value of this gum, and the following is the form used with success, and perhaps the adulterations are the best substitutes for pure caoutchouc that the cheap compound market offers.
| £ | s. | d. | |||
|---|---|---|---|---|---|
| Grind | 20 | lbs. Java, at 7d. | 0 | 11 | 8 |
| Grind | 10 | lbs. Para, at 2s. | 1 | 0 | 0 |
| Grind | 14 | lbs. White Lead, at 3d.} | 0 | 7 | 0 |
| Grind | 14 | lbs. Red Lead, at 3d.} | |||
| Grind | 1½ | lbs. Yellow Sulphur, | 0 | 0 | 3 |
| Total, | 59 | lbs. at 3d. per lb., Mill-costs, | 0 | 14 | 9 |
| Total, | 2 | 13 | 8 | ||
| Consequently costs 10½d. per lb. | |||||
This is spread upon flax cloth, (Messrs. Richards & Co., Broad Street, are manufacturers,) which weighs 10, 16, and 32 ounces to the square yard, and is about the same cost as the compound, so that the weight is the truest criterion of cost, and is so calculated by the manufactory. * * * *
Excepting garments every other description of black goods are made from such forms as I have figured, with very little variation according to the requirements of the engineer, and which needs very little judgment or experience to meet. To those who cling to these heavy goods, the formulas I have rendered will enable them to have supplies at a fair competing charge according to quality, and it is their own fault entirely if they persist in purchasing 100 per cent. of cheap powder at the same charge as for “pure caoutchouc” of a third of their density.
Your readers must be good enough not to lose the fact of “specific gravity,” and test all the above goods made with pure, unadulterated India-rubber, by their floating on water. Any deviation from this is a proof of some cheap stuff unfairly introduced. It will be just in proportion as they keep themselves well posted up in this matter, that manufacturers will be sly of throwing into their caoutchouc such mad and infamous proportions of cheap adulterations, and drive them (for they will not volunteer) to the necessity of manufacturing from the pure gum, and thus place better disposed traders upon a more just footing, and enable the latter to compete (if need be) upon their own terms, or upon recipes supplied by the engineer. Another fact must not be lost sight of, and that is the use of “light carbonate of magnesia,” which, mixed with the gum, does not increase its density, as will in some measure be illustrated by the recipe I shall now figure out, merely remarking that a somewhat heavy carbonate was used, as well as in an unroasted, and hence the somewhat increased density. This article is worth the attention of buyers of rubber goods, as in a moderate quantity it reduces the costs without correspondingly injuring the manufacturer. (Light buffer spring just sinks in water.)
| Grind together | 25 | lbs. Clear Java Rubber, |
| 5 | lbs. Para Rubber, | |
| 10 | lbs. Common Magnesia, | |
| 25 | oz. Pure Sulphur. | |
| Costs 19 cts. per pound—Sells for 60 cts. per pound. | ||
This is brown at first, but in a few days the sulphur blows over the surface grey or white, and would lead an amateur to judge they were of that color throughout. Buffer springs and other moulded goods from this compound are a little heavier than Messrs. Mackintosh and Co.’s. A density railway spring, at 4s. per lb. gross, and were made at first to meet it, also sold at 2s. 6d. per lb. net. It is a most useful spring, and in competition should be bought at 1s. 3d. to 1s. 6d. per lb. net, but I should strongly recommend that engineers try a substitute of all “Java gum,” by obtaining a few away from their usual manufacturer, ON TRIAL, as I believe their quality as a spring would not be injured, and the price would be reduced, and, moreover, it would guard against the manufacturer being left tempted to do so, without reducing the charge.
For the guidance of engineers, I remark, that a spring of this quality and dimensions, 4½ × 2½ × 1, pressed to half an inch, showed 3½ tons on the dial, and one with equal quantities of oxide of zinc and magnesia, of same size, &c., indicated 1½ tons on equal pressure, while the quality of Mackintosh and Co.’s, referred to before, and of which this was an intimation, marked 1¾ tons on the dial; of course, a spring with a smaller bore than 2½ inches would show greater tonnage.
The next recipe is for grey packing, which is largely and exclusively used by some dealers for marine engines, &c., as well as in sheet; and if the price (3s. 6d. per lb.) was not excessive for so much adulterated matter, I would pass it over in silence as a very fair and useful article, and if approved, my form will enable the engineer to obtain it much cheaper by competition.
Say then,