290 Mr. J. Denham Smith on the Detection and Estimation 



to offer satisfactory results. It would be useless to describe 

 these unsuccessful trials ; I therefore at once proceed to ex- 

 plain the mode I ultimately adopted for detecting and esti- 

 mating the proportion of colophony contained in the various 

 specimens of oil. 



I found that when colophony was dissolved in pyroxylic 

 spirit, the solution gave a bulky white precipitate, on the ad- 

 dition of acetate of lead also dissolved in pyroxylic spirit ; but 

 that when unadulterated commercial linseed oil was digested 

 with this solvent, the clear solution when cold was merely 

 rendered turbid on the addition of the spirituous solution of 

 acetate of lead. Discovering that pyroxylic spirit exerted a 

 very marked solvent action on the precipitateabove-mentioned, 

 and that the supernatant, or filtered solution, gradually de- 

 posited more of this precipitate, after standing for some time 

 or when gently evaporated, I had recourse to the common 

 rectified spirit of wine, about sp. gr. *832, which although it 

 is capable of dissolving this compound of resin and oxide of 

 lead, yet does so in almost an inappreciable quantity, espe- 

 cially if the spirit be cold. 



Having dissolved 30 grs. of common rosin in a small por- 

 tion of linseed oil, by the assistance of heat, about 3 fluid 

 ounces of rectified spirit of wine were poured upon the oil, 

 and thoroughly mixed with it by agitation ; this was boiled 

 for two or three minutes, and then allowed to cool and the 

 oil to subside; the next day the clear spirituous solution was 

 poured off, about the same quantity of fresh spirit added to 

 the residual oil, and the mixture agitated and boiled as be" 

 fore ; when bright this solution was decanted and mixed with 

 the former, the remaining oil again treated with about an 

 ounce of spirit, and this solution added to the others ; a 

 fourth time spirit was added, but this solution gave no preci- 

 pitate with acetate of lead; this agent merely rendering it 

 turbid, as in the case of pure linseed oil when dissolved in 

 spirit; from this I concluded that the whole of the resin, 

 which the rectified spirit was capable of separating, was ex- 

 tracted from the oil. The three solutions when mixed were 

 of a light yellow colour, and perfectly clear, when on the ad- 

 dition of a freshly prepared solution of acetate of lead in 

 rectified spirit the characteristic bulky white precipitate fell. 

 At the expiration of four-and-twenty hours this was collected 

 on a filter weighing 1 1*7 grs., and washed with cold rectified 

 spirit until the washing left the merest perceptible stain when 

 evaporated in a porcelain dish ; I then dried the precipitate on 

 folds of bibulous paper, and finally with a gentle heat, until 

 it suffered no decrease of weight, when the weight of the pre- 



