152 ADIIESIVES. [V. 



retard it in some points, by leading it too closely in the track 

 of that substance, whereas its peculiarities should in some 

 respects open a new path in its applications and mode of 

 application. 



The properties of guttapercha led early to the proposition 

 to apply it to ships and other apparatus requiring to be water- 

 proof, and Forster suggests an improvement for coating 

 plank (Lond. Journ. xxxvi. 31), for sheathing vessels, &c. 



For an account of guttapercha and its applications, see 

 Proc. Brit. Assoc, and London Athenaeum, 1849 ; also Amer. 

 Journ. (2) vii. 276. 



3. Adhesives. 



Textile and sheet fabrics, and solid tissues, are either orna- 

 mented or united by varnishes and cements. These have 

 either a resinous basis, or are composed of gums or glue. The 

 solvents for resins are alcohol, or the oils, whether fat, es- 

 sential, or empyreumatic ; water is the vehicle for conveying 

 gum and glue. Resins and balsams are first introduced. 



Copaiva Balsam. — Posselt (Liebig's Annalen, Ixix.) has 

 examined a copaiva balsam, from South America, which is 

 quite distinct from the ordinary kind. It has the same odor, 

 but is lighter colored and more fluid. Spec. grav. 0.94. Be- 

 comes turbid on the addition of potassa solution or of aqua 

 ammonia, but separates in time without having become soapy. 

 In alcohol it is partially soluble, forming a milky liquid. By 

 distillation with water, it yields 82 per cent, of paracopaiva 

 oil (CjoHg), the residuum being a resin, part of which is soluble 

 and the rest insoluble in alcohol. 



Rosin, or Common Resin. — Louyet (Comptes Rendus, xxiv.) 

 has obtained, by the destructive distillation of the resin of the 

 pinus maratima, two products, one of which he proposes as a 

 substitute for oil of terpentine. One is a fat oil, and the 

 other a very fluid essential oil. The latter, by rectification 

 over lime to separate acetic acid, water, &c., becomes suitable 

 for purposes both of illumination and painting. E. N. Kent, 



