8<>0 ESSENTIAL OILS. 



these solutions have an acid re-action. The pinates of potash, 

 soda and ammonia dissolve in water, but are precipitated by an 

 excess of alkali or the addition of any alkaline salt. The pinates of 

 other bases are insoluble in water, and maybe precipitated from 

 alcoholic solutions of the alkaline pinates by double decompo- 

 sition, employing an alcoholic solution of the other salt ; they 

 are most frequently insoluble in alcohol, but many dissolve in 

 ether. The composition of pinic acid was found by Rose to be 

 C 40 H 32 O 4 , or the same as that of colophony (C 40 H 30 O 4 , accord- 

 ing to Liebig). Sylvic acid has likewise the same compo- 

 sition. 



By distilling or heating pinic acid, a new resin is formed, 

 colopholic acid, of the same composition, but possessing a 

 stronger affinity for bases. 



Beta-resin (sylvic acid). The insoluble residue treated with 

 boiling alcohol, dissolves entirely; it is filtered hot, and crys- 

 tallizes on cooling. It is purified by a second crystallization, 

 particularly from alcohol containing a little sulphuric acid. It 

 is transparent and colourless, crystallizes in rhomboidal prisms, 

 terminated by four facets, which are generally very thin, and so 

 large as to resemble tables. It fuses below 2 1 2, is insoluble in 

 water, but dissolves easily in alcohol, ether, the fixed and vola- 

 tile oils. Alcohol of 72 per cent takes up, when boiling, one 

 third of its weight, but abandons nearly the whole on cooling 

 in a crystalline form. It is dissolved by concentrated sulphuric 

 acid, and precipitated again by water from that solution, but in 

 the condition, according to Unverdorben, of pinic acid. The 

 sylvates of potash, soda and ammonia are soluble in water ; the 

 sylvates of other bases are insoluble in water, but frequently 

 dissolve in ether and even alcohol. The sylvate of magnesia, in 

 particular, is soluble in alcohol. The addition of ammonia, 

 even in excess, to the solution of sylvic acid in alcohol does not 

 throw down a precipitate, and the acid precipitated by water 

 dissolves readily in ammonia ; so also does the resin in caustic 

 potash, but an excess of the latter throws down a subsylvate of 

 potash, a compound very slightly soluble in an excess of base. 

 The composition of sylvic acid is C 40 H 30 O 4 , or half these num- 

 bers, according to Tromsdorff. 



These two resins form the large proportion of colophony, but 

 a third resin has been observed in it, which is indifferent, 



