332 Mineral Substances of Organic Origin. Guyaquillite. 



derable quantities on the site of ancient forests of resiniferous 

 trees; in which case the connexion with oil of turpentine 

 would be at once beautiful and easily understood ; but if it 

 occur, as is said to be the case, in extensive layers, its imme- 

 diate source is not so easily understood. Were it volatile 

 without decomposition we could also account for its sublima- 

 tion like sulphur, or its distillation like petroleum by the 

 agency of the volcanic heat so extensively diffused beneath the 

 iSouth American continent ; but as the affinity of its elements 

 appears to be overcome by a comparatively moderate tem- 

 perature, we must still remain in doubt as to whether in its 

 present state it is to be considered as more immediately or 

 more remotely of vegetable origin. At the same time it is 

 worthy of remark, that this is not the only instance of a true 

 resin being said to occur in large quantity as a mineral pro- 

 duct in South America. I have in my possession a specimen 

 of a peculiar dark-coloured resin, which, as my friend Mr. 

 Fryer of Whitley-house, informs me, is found in a species of 

 pitch lake in the desert of St. Juan de Barengela, and is 

 thence transported in large quantities to the coast for the use 

 of the shipping. Of this substance I shall give a description 

 and analysis in a future communication. 



Guyaquillate of Silver. — To determine the atomic weight 

 of this resin, I prepared several portions of the salt of silver. 

 It appears, however, to form, in common with most of the 

 acid I'esins, both neutral or acid and basic salts, as I have been 

 unable in the several trials which the quantity of the substance 

 at my disposal permitted me to make, to obtain two portions 

 of preciselj^ the same constitution. This may also have arisen 

 partly from the necessity I have been under of using the less 

 pure variety for solution, as my supply of the unmixed was 

 exhausted. The mixture however consists in great part of 

 a bituminous matter insoluble in alcohol. 



1. Of a portion which had subsided gradually on the ad- 

 dition of ammonia and was perfectly black, 6*7 19 grs. left 

 4*728 grs. of metallic silver = 75*573 per cent, of oxide. 



2. A portion of a second preparation gave only 68*86 1 of 

 oxide ; but this was evidently a mixture, for when boiled again 

 in alcohol and collected on the filter it gave 72*266 per cent, 

 of oxide of silver. These two results indicate an equivalent 

 = ^ (C20 Hj3 O3), since a compound represented by \ (Cgo 

 H13O3) +AgO would contain 74*512 per cent, of oxide. 



3. The hot alcohol in which No. 2 was boiled, deposited 

 on cooling a brown precipitate, which gave on burning only 

 14*939 per cent, ofoxide of silver. 



