610 CONIFERS. 



Tirol/ observed that when a growing larch stem was sawn through, the 

 resin flowed most abundantly from the heart-wood, and in smaller 

 quantity, though somewhat more quickly, from the sap-wood, and that 

 the bark contained but few resin -ducts. The practice of closing the 

 cavities is adopted, not only for the sake of preserving the wood 

 and for the greater convenience of removing the turpentine, but 

 also because it tends to maintain the transparency and purity of the 

 latter. 



Description — Venice turpentine is a thick, honey-like fluid, slightly 

 turbid, yet not granular and crystalline ; it has a pale-yellowish colour 

 and exhibits a slight fluorescence. Its odour resembles that of common 

 turpentine, but is less powerful ; its taste is bitter and aromatic. When 

 exposed to the air, it thickens but slowly to a clear varnish, and hardens 

 but very slowly when mixed with magnesia. Larch turpentine, though 

 common on the Continent, is seldom imported into England,^ and the 

 article sold for it is almost always spurious. 



Chemical Composition — Larch turpentine dissolves in spirit of 

 wine, forming a clear liquid which reddens litmus ; hot water agitated 

 with it also acquires a faint acid reaction, due to formic and probably 

 also to succinic acid. Glacial acetic acid, amylic alcohol, and acetone 

 mix with it perfectly. By distillation it yields on an average 15 per 

 cent, of essential oil of the composition, C^^^H^^, which boils at 157° C, 

 and when saturated with dry hydrochloric acid gas, easily produces 

 crystals of the compound C^*^H^^ + HCl. The residual resin is soluble 

 in two parts of warm alcohol of 75 per cent., and more copiously in 

 concentrated alcohol. 



Two parts of the turpentine diluted with one of benzol or acetone 

 deviate the ray of polarized light 9 "5° to the right. The essential oil 

 deviates 6'4° to the left; the resin perfectly freed from volatile oil and 

 dissolved in half its weight of acetone, deviates 12"6° to the right in a 

 column 50 mm. long. 



We have not succeeded in preparing a crystallized acid from the 

 resin of Venice turpentine, although its composition according to Maly 

 (1864) is the same as that of American colophony, which is easily trans- 

 formed into crystallized abietic acid. 



Uses — Venice turpentine appears to possess no medicinal properties 

 that are not equally found in other substances of the same class, and as 

 a medicine it has fallen into disuse. But in name at least it is in fre- 

 quent requisition for horse and cattle medicines. 



Adulteration — Alston (1740-60) said of Venice turpentine' that it 

 is seldom found in the shops, — a remark equally true at the present day, 

 for but few druggists trouble themselves to procure it genuine. The 

 Venice turpentine usually sold is an artificial mixture of common resin 

 and oil of turpentine, which may be easily distinguished from the pro- 

 duct of the larch by the facility with which it dries when spread on a 

 piece of paper,* and by its stronger turpentine smell. 



^ Botaniaclie Zeitung, xvii. (1859) 329, barrels imported from Trieste being offered, 



abstracted in the Jahresberickt of Wiggers, 14 July, 1864. — D. H. 



1859, 18. ^ Lectures on the Materia Medica, Lond. 



^ On one occasion I observed Venice Tur- ii. (1770) 398. 



pentine in a public drug sale in London, 21 * Thus if a thin layer of true Venice tur- 



