CHAPTER LXII.
DEFECTS, IN THE COMPOSITION FOR BALLOONS, REMEDIED.
ALSO ON THE COCHUC-VARNISH.
Section 320. BALLOONS are defective in the Composition for the Varnish; which, till lately, was incapable of rendering the Balloon completely and durably Air-tight.
321. It was sometime ago reported at Paris, that Mr. Dutourny de Villiere had undertaken to construct a Balloon so truly impèrmeable, that he woud warrant the Duration of it, for several Weeks in the Air.
And it is since known that this Desideratum of the Art has been effected, in the Composition for the celebrated Balloon of Messrs. Auban and Vallet, first made subject to Direction.
322. Mr. Berniard, a French Chymist, has made curious tho’ unsuccessful Experiments, in order to melt the cochuc or elastic Bottle; as may be seen in the 17th Volume of the “Journal de Physique.”
Mr. Faujas and others made similar Trials.
323. The Writer, unacquainted with what had then been done in this Matter, coud not help remarking the striking Properties of the Cochuc in its present Form, to answer every Intention of the best Varnish, if its Price was lower;—viz. compact, pliant, unadhesive, and unalterable by Weather;—if it coud be dissolved, and afterwards made to recover its present unadhesive Form: an Art in which the East and West-Indians are still our Masters.
He has, however, after expensive Trials and Combinations, been able to reduce it into a limpid Liquor.
As it may prove a useful Ingredient for Air-tight Varnish; the Secret he now discovers to the World: and it is merely this.
324. “Take any Quantity of the Cochuc, as two Ounces Averdupois: cut it into small Bits, with a Pair of Scissars.
Put a strong Iron-Ladle (such as Plumbers or Glaziers melt their Lead in) over a common Pit-Coal or other Fire.
The Fire must be gentle, glowing, and without Smoke.
When the Ladle is hot, much below a red Heat; put a single Bit into the Ladle.
If black Smoke issues, it will presently flame, and disappear: or it will evaporate without Flame: the Ladle is then too hot.
When the Ladle is less hot, put in a second Bit, which will produce a white Smoke.
This white Smoke will continue during the Operation, and evaporate the Cochuc: therefore no Time is to be lost: but little Bits are to be put in, a few at a Time, till the whole are melted. It shoud be continually and gently stirred with an Iron or Brass Spoon.
The Instant the Smoke changes from white to black, take off the Ladle; or the whole will break out into a violent Flame, and be spoiled or lost.
(Care must be taken that no Water be added: a few Drops only of which, woud—on Account of its superior specific Gravity, for the Cochuc swims in Water—make it boil over furiously, with great Noise.)
At this Period of the Process; two Pounds, or one Quart of the best drying-oil, (or even of raw Linseed-Oil, which, together with a few Drops of Neat’s-Foot-Oil, must have stood a Month, or not so long, on a Lump of Quick-Lime, to make it more or less drying)—being poured off the Lime-Lees; is to be put into the melted Cochuc, and stirred till hot: and the whole poured into a glazed Vessel, throu’ a coarse Gauze, or fine Sieve.
When settled and clear, which will be in a few Minutes; it is fit for Use, either hot or cold.
The Silk shoud be stretched all Ways horizontally, by Pins or Tenter-Hooks, on Frames; which Frames, the greater they are in Length, the better: and the Varnish poured on cold, in hot Weather; and hot, in cold Weather.
It is perhaps best, always to lay it on, when cold.
The Art of laying it on properly, consists in making no intestine Motion in the Varnish, which woud create minute Bubbles. Therefore Brushes of every Kind are improper.
Each Bubble breaks in drying, and forms a small Hole, throu’ which the Air will transpire.
