22 



WOOD TURPENTINE. 

 Constants of commercial gum and wood turpentines. 



1 Emergent stem thermometer; uncorrected. 



2 Wjiss solution. Stood one-half hour; 200 per cent excess iodin. 



From these figures it is quite evident that both steam-distilled and 

 destructively distilled turpentines have many of the same general 

 characteristics as gum spirits. A point of considerable interest, in 

 view of the often-repeated complaint of painters that wood turpentine 

 is strongly acid and because of this is very trying to the eyes, is the 

 comparative acid numbers of the several classes of turpentine. 

 There is no evidence to indicate that the acidity of wood turpentine is 

 greater than that of gum spirits, though of course the acids may not 

 be the same. The acid and saponification numbers are indicative of 

 the amount of oxidation products which are present. These figures 

 are not so striking, however, as is the iodin number discussed below. 

 While it is true that the limits of specific gravity and of the quantity 

 distilling below 170 C. do not differ widely among these three classes of 

 turpentines, it is also true that the specific gravity will average higher 

 and the quantity distilling below 170 C. lower in wood turpentine 

 than in gum turpentine. In other words, the wood turpentine now 

 on the market does contain too much pine oil distilling above 170 C., 

 and to this fact, chiefly, is undoubtedly due the dissatisfaction which 

 is expressed with reference to its drying properties. 



The iodin number also throws light on the composition of the tur- 

 pentines. It indicates that in certain cases the oil contains large 

 quantities of constituents other than pinene or other terpenes of the 

 same formula. In other words, the iodin number indicates practi- 

 cally what a distillation does that is, the approximate quantity of 

 heavy oils present. It will be seen from Table 2 that, compared with 

 good gum spirits or with the light oils from crude wood turpentine, 

 the heavy oils have a low iodin number; the iodin number therefore 

 shows whether or not the sample contains considerable quantities of 

 heavy oils, and also that these heavy oils are not of the same nature 

 as the light oils. The same fact is shown in a general way by the 

 saponification number. Those turpentines which have large resi- 

 dues that do not distill below 185 C. have high saponification num- 



