64 



general formula for the terpene hydrocarbons (of which ordinary 

 American or French turpentine may be cited as typical examples) a 

 closer examination of this substance showed that it was clearly not a 

 terpene. It had a specific gravity of 0-8046 at if /if and 0-8020 

 at 2O/2O. Its boiling point was i66-i68 C. under atmospheric 

 pressure, and it exerted no action on the plane of a ray of polarised 

 light. It was a colourless and very mobile liquid, having a penetrating 

 but not unpleasant odour, somewhat suggesting yet quite distinct 

 from that of the hop oil itself. A study of its chemical and physical 

 characters showed it to be an unsaturated, open-chain hydrocarbon, 

 and a careful comparison of its properties with those of myrcene, a 

 hydrocarbon first obtained by POWER and KLEBER from bay oil, proved 

 it to be identical with that substance. In all the samples of oil with 

 which I worked myrcene was present to the extent of 40 to 50 per 

 cent., although for the reason given below it will be seen that this is 

 liable to considerable variation. It is well known that when hops are 

 kept for a long time at ordinary temperatures, their aroma suffers 

 marked deterioration, and their " stickiness " when rubbed between 

 the fingers greatly diminishes. It is also known that when hop oil is 

 stored in such a way (e.g., in an ordinary partially filled bottle) that 

 air has access to it, the oil becomes more and more viscous and its 

 solubility in alcohol diminishes. These phenomena, which are of 

 considerable technical importance are due to the change of the 

 myrcene present, for this compound possesses in a very marked degree 

 the property of absorbing oxygen from the air, and of becoming 

 quickly converted into a hard colourless resinous mass, polymerisation 

 changes taking place at the same time. I shall allude a little later to 

 the bearing of this fact on the brewing process. 



The Second Fraction. This was very small, and from 600 c.c. of 

 oil (the largest quantity with which I worked at one time) only 

 amounted to a few cubic centimetres. It was a colourless and very 

 fragrant liquid, having a sp. gr. = 0-8571 at 2O/2O, and a composition 

 corresponding with the formula C 10 H 18 O. It had a very slight laevo- 

 rotatory action on the plane of a ray of polarised light, and evidently 

 consisted of inactive linalool, an alcoholic body occurring in the 

 oil of linaloes and in some other essential oils. The slight optical 



