To the amateur chemist bladders often form an efficient substitute for a much more expensive apparatus. They form the cheapest and most convenient gasholders that can be obtained; and we have often melted platinum, burned small pieces of iron, and even produced a good lime-light by means of two bladders and some very simple home-made apparatus. Strips of bladder, after being moistened, adhere firmly to glass and metal in drying, and often form the best joints and lutes in putting pieces of apparatus together. And in certain physical experiments on liquids, pieces of bladder are as convenient an article as can be used.
Bladders are prepared by being first freed from all fat and flesh. This is best done by blowing them up and removing all superfluous matter with a sharp knife, the utmost care being taken to avoid cutting the bladder itself, since the least puncture renders the bladder worthless. It is always well to expand the bladder a little first, as if we begin to cut while the bladder is thick and unexpanded the danger of cutting the bladder itself is greatly increased. The bladder should then be soaked in a weak solution of common washing soda and well washed, after which it is blown up as tightly as possible. and the neck firmly tied. It is now to be rolled and worked with the hands on a smooth board or table, and as fast as it gets larger so that the air does not keep it tight, it must be blown up again. The use of a bladder-tube and stop-cock greatly facilitates this operation, as the bladder can then be frequently filled without the trouble of tying and untying the neck. The blowing up of a large bladder is a somewhat tedious operation, but it is astonishing to see the extent to which it may be increased in size. After being blown as large as possible, the bladder should be filled with water and emptied two or three times, so as to wash out the inside. This tends greatly to prevent putrefaction. After being thoroughly washed the bladder should be soaked in a weak solution of chloride of lime, or, better still, Javelle water. It should then be thoroughly emptied, blown up tight, and tied. If now well dried, it will keep in good condition for any length of time. The great difficulty with bladders when used for such purposes is that they can not be used in a dry state, and they soon become putrid if exposed to alternate wetting and drying. This difficulty may be avoided in a great measure by soaking the bladders in a solution of salicylic acid in glycerine. This not only preserves them but keeps them soft and pliable, so that they may be used quite readily for experiments on gases. By careful selection and thorough work in preparing and expanding the membrane a good-sized ox-bladder may be converted into a very serviceable gasholder.