26 SUBSTANCES SOLUBLE IN PETROLEUM SPIIUT. 



the addition of caustic potash. Any resin that may have been 

 obtained in the quantitative estimation of the oil (§ 23), should 

 be tested for a fluorescent substance by treating with distilled, or, 

 if necessary, alkaline water ; umhdUferone should be specially borne 

 in mind (§ 43). The resinous constituents, which will be sub- 

 sequently isolated according to § 3G, et seq., may be examined for 

 umbeiliferone by mixing with sand and submitting to destructive 

 distillation, or by heating in sealed tubes with alcoholic solution 

 of hydrochloric acid. 



Further, the specific gravity of ethereal oils should be taken. 

 Westphal's specific-gravity balance may be advantageously em- 

 ployed for this purpose, especially if the quantity of oil at disposal 

 is rather small. (Cf. § 141.) 



It should also be ascertained what percentage of pure alcohol 

 a spirit must contain to be miscible with the oil in all proportions. 

 A drop only of spirit is first added to the same quantity of oil, 

 and if the resulting mixture is perfectly clear, note should be 

 taken whether the further addition of spirit cause a cloudiness or 

 not. It is, however, only with freshly prepared oil that such 

 reactions can be considered as characteristic of the oil. Many 

 oils undergo a change on keeping for any length of time, becoming- 

 more or less soluble in alcohol, or forming clear mixtures with 

 small pro^iortions, but cloudy with larger (§ 141). 



§ 28. Reactions. — It is, moreover, desirable to make qualitative 

 experiments with small quantities of the ethereal oil, in order to 

 become acquainted with their behaviour to some few re-agents. 

 For this purpose I have recommended sulphuric acid, alone or 

 applied in combination with sugar, nitre, or ferric chloride ; nitric 

 acid, alcoholic hydrochloric acid, solution of bromine in chloro- 

 form, picric acid, etc. 



For the results which I myself, and some of my pupils, have 

 obtained with the more important ethereal oils, see § 142. 



§ 29. Detection of Sulphur. — Some ethereal oils contain sulphur, 

 which may be detected by mixing a few drops of the oil with 

 carbonate of soda and nitre, and introducing it into a piece of 

 combustion tubing, al^out 15 ctni. long, scaled at one end. The 

 upper part of tlie tube is then cluugcd with a similar mixture of 

 soda and nitre, and the whole ignited as if it Avere an ultimate 

 analysis in miniatuie. About one-third of the mass from the 

 bottom of the tube upwards is then dissolved in a little water, 



