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_.