74 



BALLOONING, MODERN. 



strength of material and iraperviousness may 

 thus be increased to any desired extent for this 

 reason, rubber is the only suitable substance for 

 coating balloons of extraordinary dimensions. 

 The great Giffard balloon of the Paris Exposi- 

 tion was made of several layers of cambric and 

 rubber cemented together. To prepare the rub- 

 ber solution, sheets of the elastic material are 

 suspended in barrels or cans containing benzine, 

 and a few hours will suffice to soften the gum s'o 

 that it may be stirred into a pasty mixture. To 

 this is added, from time to time, minute doses" 

 of bichloride of sulphur in benzine, taking sev- 

 eral days for the operation, at the end of which 

 time the proper coagulation may have taken 

 place. This rubber solution is applied, by means 

 of a spreading-machine, to the cloth before cut- 

 ting. Each coat is slightly dusted with steatite, 

 to give more body, and when enough coats have 

 been laid on, it may be taken from the machine 

 and rolled up. If it is to be used singly, it is 

 ready to be made into a balloon ; but if it is re- 

 quired to be doubled, the surface is left in a 

 sticky state and the faces of two pieces are pressed 

 together. The cost of rubber coating exceeds 

 that of oil varnishing; but some advantage is 

 gained in lightness and lasting qualities. 



The Valve. The imperfection of the balloon 

 valve seems to have been a considerable source 

 of annoyance, even to the French aeronauts, who 

 frequently mention the " cataplasm," or poul- 

 tice, with which 

 they are in the hab- 

 it of stuffing their 

 wooden valves to 

 make them gas 

 tight. This seems 

 a barbarous mode 

 of procedure, which 

 is indeed unneces- 

 sary, for a valve can 

 be made of metal 

 which will be per- 

 fectly free from 

 leakage without any 

 such outward appli- 

 cation, and it may 

 be as large as three 

 feet in diameter, if 



required. The best metal for the purpose is cop- 

 per, and one of the worst is brass. The latter will 

 be corroded by contact with the gas, while the 

 former will not. The size of the valve must bear 

 some proportion to that of the balloon,from twelve 

 to twenty-four inches diameter being sufficient for 

 ordinary ones. A valve twelve inches in diam- 

 eter is large enough for a balloon of 25,000 cubic 

 feet capacity. The smallest of these need not 

 weigh, more than three pounds. They are made 

 of rolled sheet copper, and consist of a U-shaped 

 rim, a cross bar, two clappers, a bridge, and a set 

 of rubber springs. The clappers of the valve are 

 covered with soft leather, and a projecting edge 

 on the rim and cross piece presses the leather 

 into a groove near the edges of the clappers. 

 The largest valves would gather so much water 

 in case of rain that it is recommended to have the 

 clappers as nearly flush as possible with the upper 

 part of the rim instead of the lower, an arrange- 

 ment that adds somewhat to the*ost of its con- 

 struction, but obviates the danger of having the 



SMALL 



VALVE. 



valve opened by an accumulation of rain. It is 

 well to have the clappers of this style of valve 

 worked xip into a bulging form, from the groove 

 to the center, in order that they may be some- 

 what stiffened. The sharp edge, which is fitted 

 into the groove of the clapper, will be placed, in 

 this valve, at the upper edge of the rim, but bent 

 downward to meet the groove. Staples are on 

 the under side of the clappers, to which cords 

 are attached, forming a loop or loops for con- 

 necting the valve cord, which passes down through 

 the neck of the balloon into the car. 



To insert the valve, we have simply to draw 

 the leather collar in the top of the balloon over 

 the lower flange and around the rim, securely 

 lashing it in its place. The upper edge of the 

 collar is then turned down, and another lashing 

 is made over it, to which are tied eight cords, 

 arranged at equal distances apart, forming the 

 net attachments. 



The Net.-^-This is not so difficult to make as 

 is generally thought. It is begun at the top or 

 center, continued downward, and at the lower 

 edge merges into tabs, to which are attached the 

 ropes proceeding to the concentrating ring. A 

 net must not only be strong enough to bear the 

 load that the gas will lift, but must be equal to 

 the strain brought upon it by the wind during 

 inflation. It is of especial importance that the 

 net should be strong enough at the top, near the 

 valve, where the meshes must be small, so that 

 if a break occurs in one it would not extend eas- 

 ily to the rest. The top is really the weak part 

 of the net, particularly for captive balloons. 

 Several instances are known of balloons passing 

 through their nets from meshes breaking at the 

 center, but fortunately no captive balloon has 

 ever met with this accident while in the air, 

 although it is liable to occur at any time if due 

 care is not taken. Cotton twine makes the best 

 net ; silk would of course be light, strong, and 

 soft, but its costliness puts it out of the question, 

 except for special cases. Flax or hempen cord, 

 though strong at first, soon weakens, and when 

 wet with rain will shrink several feet, making a 

 close-fitting net too small for the balloon, while 

 under similar circumstances, cotton shows little 

 or no change. The strength of twine required 

 must be determined by the size of the balloon. 

 For the smaller ones, a mesh should not break 

 with a weight of seventy-five pounds, and for 

 the largest it should bear two hundred pounds. 



At a convenient height suspend a hoop, and 

 tie on it, say, one hundred loops, each about 

 three inches long. Begin by knitting the first 

 row to these loops, and on the succeeding rows 

 enlarge the number, by adding for the first few 

 rounds four meshes, then three, two, and finally 

 one mesh, until the number is sufficient to en- 

 circle the largest part of the balloon, after 

 which the knitting will continue to the end 

 without further increase of the number. The 

 meshes may be frequently enlarged also, accord- 

 ing to judgment. At the distance of eight or 

 ten feet from the lower edge the net divides into 

 twenty or more parts, which are knitted sepa- 

 rately, and form the tabs to which the net ropes 

 are to be attached. If two hundred meshes are 

 on the last round, and twenty attachments are 

 wanted, we begin the tab by knitting on to ten 

 meshes, then return, first making a loop or half- 



