Besides stearates of the metals, glues and gelatins have been used for proofing purposes, but owing to their stiffening effect, they are only of use in some few isolated cases. With glue and gelatin the fixing agent is either tannic acid or some metallic salt. Tannic acid converts gelatin into an insoluble leather-like body; this can be deposited in the interstices of the fabric by passing the latter through a gelatin bath first, and then squeezing and passing through the tannic acid. Bichromate of potash also possesses the property of fixing the proteid bodies and rendering them insoluble.

The following are special processes used to advantage in the manufacture of waterproof fabrics:


Ordinary Fabrics, Dressing Apparel, etc.—Immerse in a vat of acetate of alumina (5° Be.) for 12 hours, lift, dry, and let evaporate at a temperature of from 140° to 149° P.


Sailcloth, Awnings, Thick Blankets, etc.—Soak in a 7 per cent solution of gelatin at 104° F., dry, pass through a 4 per cent solution of alum, dry again, rinse in water, and dry.


Fabrics of Cotton, Linen, Jute, and Hemp.—Put into a bath of ammoniacal cupric sulphate of 10° Be. at a temperature of 87° P.; let steep thoroughly, then put in a bath of caustic soda (20° Bé.) and dry. To increase the impermeability, a bath of sulphate of alumina may be substituted for the caustic-soda bath.


Saturate the fabrics with the following odorless compound, subjecting them several times to a brushing machine having several rollers, where the warp threads will be well smoothed, and a waterproof product of fine sheen and scarcely fading will be the result. The

compound is made with 30 parts, by weight, of Japan wax, 22.5 parts, by weight, of paraffine, 12 parts, by weight, of rosin soap, 35 parts, by weight, of starch, and 5 parts, by weight, of a 5 per cent solution of alum. Fabrics thus prepared are particularly adapted to the manufacture of haversacks, shoes, etc.


White or Light Fabrics.—Pass first through a bath of acetate of alumina of 4° to 5° Bé. at a temperature of 104° F., then through the rollers to rid of all liquid; put into a warm solution of soap (5 parts, by weight, of olive-oil soap to 100 parts, by weight, of fresh water) and finally pass through a 2 per cent solution of alum, dry for 2 or 3 days on the dropping horse, and brush off all particles of soap.


Dissolve 1.5 parts, by weight, of gelatin in 50 parts, by weight, of boiling water, add 1.5 parts, by weight, of scraped tallow soap and 2.5 parts, by weight, of alum, the latter being put in gradually; lower the temperature of the bath to 122° P., lift out the fabric, dry, and calender.


Tent Cloth.—Soak in a warm solution of 1 part, by weight, of gelatin, 1 part, by weight, of glycerine, and 1 part, by weight, of tannin in 12 parts, by weight, of wood vinegar (pyroligneous acid) of 12° Be. The whole is melted in a kettle and carefully mixed. The mass is poured into the receiver of the brushing machine, care being taken to keep it liquid. For a piece of 500 feet in length and 20 inches in width, 50 to 80 parts, by weight, of this compound are needed.


To freshen worn waterproof material, cover with the following: Fifty-five thousand parts, by weight, of gelatin; 100 parts, by weight, of bichromate of potash; 100 parts, by weight, of acetic acid (to keep glue from congealing), and from 3,000 to 5,000 parts, by weight, of water; to this add 500 parts, by weight, of peroxide of ammoniacal copper, 100° Be. This compound is put on the fabric with a brush and then exposed to air and light.


Soft Hats.—The hats are stiffened as usual, then put through the following three baths: Dissolve J part, by weight, of tallow soap in from 40 to 50 parts, by weight, of warm water (140° P.). Put 3 to 4 dozen hats into this solution, leave them in it for half an hour, then take out and put them as they are into another bath prepared with 40 to 50 parts, by weight, of water and 0.5 part, by weight, of alum and heated to 86° to 104° F. After having been left in the second bath for 0.25 or 0.5 hour, take out as before, put into the third bath of 40 to 50 parts, by weight, of water, 0.5 part, by weight, of alum, and about 13 parts, by weight, of fish glue. In this cold bath the hats are left for another 0.5 hour or more until they are completely saturated with the liquid, then dried and the other operations continued.


Woolen cloth may be soaked in a vat filled with aluminum acetate, of 5° Be., for 12 hours, then removed, dried, and dried again at a temperature of 140° F.


Wagon covers, awnings, and sails are saturated with a 7 per cent gelatin solution, at a temperature of 104° F., dried in the air, put through a 4 per cent solution of alum, dried again in the air, carried through water, and dried a third time.