Engineers do not seem sufficiently alive to this question of density. Of course in colored articles, it is necessary to use some pigment, but it is the monstrous excess that I wish to expose, and applies more particularly to the American inodorous system. I think it only fair to Messrs. Mackintosh & Co., to admit, that most of their goods I have examined float on water; but I know nothing, and have no interest whatever in their establishment, but simply state the fact, because I have found they form the exception to this adulterating or mixing system.

What I wish more especially to impress upon the minds of engineers, is the ready mode they have of discovering or ascertaining whose make is best and cheapest, and it is more likely an India-rubber valve of same dimensions at 2s. 6d. per lb., will cost more money than one at 4s. 6d. per lb., arising solely from the extravagant mixture of these cheap pigments, and its great density over the latter. Java India-rubber, which is mostly used, is at this moment about 7d. per lb., and best Para sheet about 1s. 11d. * * If they are fair goods for usual work, then I trust the information I supply may enable contractors to obtain their wants by competition, furnishing their own form. This will realize a great saving to them; but they must not be induced to accept goods of greater density under the plea of being better. The Java gum used in these adulterated articles is ground without undergoing the process of cleansing, but in all articles of light density, the cleaning machine frees it from all gritty matter, and it is usually employed in this cleansed state for such, as well as all gray or white goods.

Messrs. Mackintosh & Co., claim in their patent for vulcanizing all the preparations of sulphur, and without it, so far as I know and believe, no substitute has yet, or is likely to be discovered at a price which can render it commercially available. Indeed, I doubt whether any other than sulphurous bodies will vulcanize, or render fit for the use of the engineers the gum called India-rubber. Hence, the reason why many of the manufacturers are licensed under that firm, and subject to have their goods so stamped. The American inodorous makers attempted to shield themselves, (but on legally trying the point) in vain. The screen against Mr. Mackintosh’s patent was called, as a blind, “hypo.” It is prepared in several ways, but is a compound of sulphur and lead, and when perfect and the lime well washed away, is a very excellent black, costing about 30s. per cwt.; but its whole efficacy rests with the sulphur, and without it would not vulcanize, (though lead works kindly with caoutchouc). This chemical contains about 20 per cent., of sulphur, consequently, five pounds is about equal to twenty-five ounces of sulphur. This extra cost was readily submitted to, rather than to knuckle under to Messrs. Mackintosh’s patent. In many cases it was only said to be used, and what really was used, was white lead or lampblack, oxide of zinc, all in connection with sulphur, according as the color of the goods required, rendered necessary. It was pretended also, by these inodorous manufacturers, that white goods, such as the elastic beds, advertised as “Improved Hydrostatic Beds,” and “Hospital Sheeting,” were vulcanized with sulphuret of zinc, prepared chemically; when, in fact, it is well known that the cost of manufacture is quite prohibitory, and is only of value in proportion to its richness in sulphur. What was in reality used, was, and is, the “yellow sulphur,” and the “pure precipitate of that article.” I mention these things to clear the mystification it may be to the interest of manufacturers to keep up, and as I only write from experience, I have reason to believe your readers, who are interested, will better understand the nature and value of unmixed and mixed caoutchouc, after my fund on this topic is exhausted. With these remarks I will give the recipe for common black packing at 2s. 2d. per lb., in quantity, discount as agreed.

The chemical termed “hypo” is manufactured thus: The sugar of lead is made into a solution with water in a separate vessel. The sulphur and lime are then boiled in water, so as to make a solution of sulphur with the lime. The latter solution (clear) is then poured into the former, which unites with the sulphur, and the precipitate is the “hypo.” The hypo is then washed and dried. The lime merely enables the lead to take up the sulphur.

£s.d.
Grind15lbs. Java Caoutchouc at 7d.089
Grind15lbs. Para Caoutchouc at 2s.1100
Grind15lbs. Oxide of Zinc at 3d.040
Grind16lbs. China or Cornwall clay003
Total,16lbs.
28oz. Yellow Sulphur003
Mill-costs at 3d. per lb., on 73 lbs.0183
Total, 353
Costs therefore, 10½d. per lb.

The above is 110 or 112 per cent. of adulteration.

I should here remark, there is also a kind of packing in use, which perhaps is practically best known as “Rag Packing,” made principally from the useless cuttings in the manufacture of India-rubber coats, where the gum is run or spread on calico foundations, which is usually the case with water-proof garments offered for sale at the shops. It is made as follows:

Rag packing for valves, bearing springs, or in sheets of any thickness, where less elasticity is required, and great pressure.

£s.d.
Grind35lbs. Useless scraps, say030
Grind18lbs. Black Lead, at 2¼d.034½
Grind16lbs. Java Gum, at 7d.094
Grind1lbs. Yellow Sulphur,001½
Total,70lbs.
Mill-costs at 4d. per lb. on 70 lbs.134
Total, 1192

This is sold at 2s. per lb. in very large quantities, or 1s. 6d., if a shrewd man, net, or a small discount for cash.