Glue, gelatine, animal charcoal, phosphorous, cements, pastes and mucilages

by F. Dawidowsky

Preparation of Gelatine from Ordinary Glue.

For this purpose ordinary pale-colored glue is allowed to swell up for two days in cold strong vinegar. The vinegar is then drained off and the glue which is now almost colorless, is placed upon a sieve and allowed to float in a vessel filled with water for 10 to 12 hours. It is then placed upon a linen cloth, stretched in a room heated to at the utmost 68° F., allowed to drain and dry to such an extent that on heating it to between 158° and 167° F., a thick clear liquid is obtained. This liquid is carefully poured upon plates of glass or marble, so as to avoid the formation of air bubbles and when solidified the leaves are removed and completely dried in the air. The product thus obtained being entirely tasteless and almost colorless may be used in the preparation of jellies, as well as for foils for pictures, etc.

Preparation of Gelatine for Photographic Printing and for Photographic Purposes in General.

Gelatine suitable for this purpose should be colorless and free from all salts, since the latter would exert a disturbing effect upon the chemical processes which take place during the photographic operation. For the removal of the salts the gelatine is treated as follows: Colorless gelatine of the best quality is broken into small pieces and covered with 10 to 12 times the quantity of water, the latter being changed every 15 to 20 minutes until the last water shows no trace of lime, which is known by adding to the water solution of oxalate; the absence of turbidity indicates that the water is free from lime. The white of an egg is now mixed with five drops of ammonia and twice the volume of distilled water and shaken to froth in a bottle. This quantity suffices for 6 to 8 ozs. of gelatine. The washed gelatine is next melted in a dish and mixed with the white of egg. One part of glacial acetic acid mixed with 250 parts of water is then added drop by drop, stirring constantly until sensitive litmus paper shows an acid reaction. The liquid is now rapidly brought to the boiling-point, whilst stirring constantly, and then filtered in a warm place to avoid gelatinization. The gelatine now contains only the salts of the white of egg, some ammonium acetate and free acetic acid. For their removal the solidified gelatine is cut into pieces, which are placed in water.

Gelatine Capsules for Medicinal Purposes.

Considerable use is made of gelatine in medicine. To disguise the disagreeable taste of some medicines they are either mixed with gelatine solution or inclosed in gelatine capsules. To prepare the latter, dissolve 8 parts of gelatine, 2 of sugar, and 1 of gum-arabic in 8 of water in a water-bath, and dip the pear-shaped ends of iron rods into the lukewarm solution. To facilitate the detaching of the gelatine film from the rods, grease the pear-shaped ends with oil. The capsules are dried by placing them in holes of a corresponding size in boards. When dry they are filled with the respective medicine, and closed with a drop of the same solution.

Court Plaster.

Gelatine or isinglass 155 grains, alcohol 13½ fluid drachms, glycerine 15½ grains. Water, tincture of benzoin, each a sufficient quantity. Dissolve the gelatine in a sufficient quantity of hot water to make the solution weigh 4½ ozs. Spread one-half of this in successive layers by means of a brush upon taffeta stretched upon a frame so as to present a level surface, waiting after each application until the layer is dry. For the first two applications the gelatine solution should be warmed merely to above its congealing point, so that when spread out it may rapidly solidify and at the same time adhere to, but not pass through the fabric. Mix the second half of the gelatine solution with the alcohol and glycerine, and apply it in the same manner. Then reverse the taffeta, coat it on the back with the tincture of benzoin and allow it to become perfectly dry. The tincture of benzoin applied to the reverse side leaves a thin layer of resin which in a measure renders the plaster water-proof; it is, however, advisable to repeat this application once or twice. The addition of glycerine to the last portion of the gelatine solution prevents the plaster from breaking, and preserves its flexibility for a long time. When the plaster is dry it is cut in pieces of suitable length and preserved in well-closed vessels.

Gelatine Foils.

Large quantities of gelatine foils, which are leaves of gelatine about as thick as a sheet of paper, are produced in England and France where their manufacture forms a special branch of industry. They are either simply colored or printed with neat designs in gold or silver.