14 FISH ISINGLASS AND GLUE. 



ill modern plants, a type of evaporator used has revolving steam 

 coils ; the solutions are thereby uniformly heated and undue frothing 

 from local superheating is prevented. The distilling head is pro- 

 vided with baffle plates and is connected with a vacuum pump and 

 condenser. To conser^^e fuel, the steam from one evaporator is led 

 through the coils and jacket of the next in a series, on the principle 

 of multiple effect. After concentration to the desired consistency 

 (fish glue contains usually about one-half its weight of water) the 

 product (fish glue) is run while still hot through cloth filters into 

 a receiving tank. 



Since fish glue generally does not yield a very good jelly when 

 cooled, on account of the presence of impurities, it is employed as 

 liquid glue. To prevent the glue from gelatinizing at room tempera- 

 tures an acid such as hydrochloric or acetic acid is added, and the 

 adhesiveness of the material is little affected. Since it is not required 

 that this liquid glue be heated or be applied to hot surfaces, there has 

 been a reasonably large demand for it. It has been largely used as 

 a size for straw goods, especially where it has been treated with sul- 

 phurous acid, since this latter agent bleaches the straw; it is also 

 employed as a size for textiles. Good grades of fish glue are used for 

 court-plaster, but isinglass is a better adhesive for this purpose. The 

 greatest demand for fish glue comes from the general demand for a 

 liquid adhesive. 



Davidowsky « describes the manufacture of fish glue as follows : 



The principal point to be observed in the ruanufacture of fish glue is the 

 removal of the skin, which is effected by means of dilute sulphuric acid. After 

 the removal of the last traces of acid, the fatty matter of the fishes is saponified 

 by treatment of milli of lime frequently renewed. After washing out the lime, 

 the pulpy mass is placed in a solution of sodium hyposulphite, alum, and sodium 

 chloride, and left for a few days. The liquor is drawn off and replaced by a 

 mixture of solutions of alum, dilute sulphuric acid, and nitric acid. After 

 macerating in this mixture for a few days, the mass is thoroughly washed and 

 boiled to a glue, and the resulting product is clarified with sulphurous acid or 

 alum. 



As will be seen, the entire process requires many chemicals, and besides, the 

 yield of glue, which has no especially good qualities, is small. It is used as 

 a substitute for isinglass for clarifying. 



That the manufacture of fish glue alone is not very profitable may 

 be seen from the fact that glue manufacturers do not rely on this one 

 product as a source of profit. Thus, one Massachusetts company sells 

 large quantities of fertilizer and also cod-liver oil. Another offers to 

 the trade glue, ink, lubricating oil, paste, mucilage, and other 

 products. 



° Davidowsky, F., 1905 : " Glue, gelatin, acimal charcoal, phosphorus, cements, pastes, 

 and mucilage." Translated from the German by W. T. Brannt. Philadelphia. 



