94 Prof. Johnston on the Composition of Resins. 



formation regarding the circumstances under which they ac- 

 tually occur. 



The pasto varnish described by Boussingault* is closely 

 allied in constitution to the berengelite. This substance when 

 freed by digestion in alcohol from a little green resin with which 

 it is mixed, is colourless and possesses many of the properties 

 of caoutchouc. It is very tenacious, and stretches into thin 

 membranes, which are applied as a varnish to wooden vessels. 

 It adheres strongly and after a time hardens, but never cracks. 

 It forms a soap with caustic potash, from which acetic acid 

 separates it. When dried and heated to 130° Cent. = 266° 

 Fahr., the varnish thus separated melts, and on cooling is 

 brown, tenacious, and {no'w) soluble in all proportions in 

 alcohol, aether, and oil of turpentine. It does not appear from 

 Boussingault's paper whether the previous solution in caustic 

 potash be necessary to the production of this change, though 

 he does speak of a remarkable modification being caused 

 by caustic potash. The composition of the pure varnish (A) 

 and of the resin or modified varnish (B) are thus given, the 

 first being a mean of three, the second of two analyses. 



A. 



Carbon = 71-766 

 Hydrogen = 9 '633 

 Oxygen = 18-600 



99-999 



100-000 100-000 



The third column is calculated according to the formula 

 C40 Hg2 Og , which agrees very well with the analyses of the 

 varnish. It is not improbable however that the resin should 

 be represented by a formula somewhat diiferent. 



The pasto varnish is brought to the neighbourhood of 

 Quito from the high land of Macao, on the eastern slope of 

 the Andes, from which the waters descend to the river of the 

 Amazons. Except that it is of vegetable origin nothing 

 is known regarding it, the tribes of Indians from whom it is 

 obtained being still independent. The difference of its pro- 

 perties previously to fusion forbid the supposition that it is 

 identical with the berengelite; were a distance of 20 degrees 

 of latitude between the places from which they are respect- 

 ively brought, not sufficient to render a common origin highly 

 improbable. 



It may not be uninteresting to present here a comparative 

 view of the formula^, by which the several resins of which ana- 

 lyses have hitherto been published may be represented. 



• An, dc Chim. et de Fhysique, vol. Ivi. p. 216. 



