Mr. C. Tomlinson on the Cohesion-Figures of Liquids. 191 



cloudy. Most of these oils, when taken out of the freezing mix- 

 ture, and a drop deposited on water at + 35°, fo t rmed admirable 

 and characteristic cohesion-figures, although, certainly, some 

 of the figures which are usually active (such as that of oil of 

 cloves) were less active than at a higher temperature. 



On the other hand, the effects of a high temperature on the 

 volatile oils are very 'decided. For example, a drop of the oil of 

 bitter almonds deposited on hot water spins for a moment and 

 scatters the more fluid portions of the oil with violence around ; 

 after which the peculiar features of the cohesion-figure are dis- 

 played with rapidity. A drop of oil of lavender on hot water 

 produces its sea-weed pattern on a much smaller scale than 

 usual. 



But the effects of temperature in modifying the cohesion- 

 figures are most remarkable when an essential oil is subjected to 

 fractional distillation. The volatile oils have not, in general, a 

 fixed boiling-point, any more than a fixed freezing-point. If 

 a volatile oil, such as oil of camphor*, be heated, its boiling- 

 point will go on rising until the whole of it has evaporated. An 

 ounce and a half of this oil was distilled and the temperature 

 noted. 



At 140° F. it began to simmer. 



„ 210 „ it was boiling. 



„ 260 „ boiling briskly with spheroidal globules on the 

 surface. 



„ 300 „ boiling rapidly. 



„ 350 „ „ „ a milky fluid distilled over. 



„ 385 „ a transparent colourless fluid passing over. 



„ 390 „ boiling rapidly and distilling. 



„ 400 „ boiling. Temperature slowly rising. 



„ 41 6 „ white fumes in the belly of the retort ; transparent 

 liquid distilling over ; retort jerking. 



„ 418 „ rapidly distilling. 



„ 430 „ oil in retort deeper in colour. 



„ 460 „ limpid transparent liquid distilling over. Nearly 

 all the oil in the retort gone. 



In another operation the distillate was collected in test-tubes, 

 which were changed as soon as any alteration in its character 



* This oil, which is seldom seen in Europe, is the elaeopten, while the 

 ordinary solid camphor is the stearopten of the camphor laurel tree. The 

 specimen furnished to me through the kindness of Messrs. Baiss Brothers, 

 of Leadenhall Street, London, is of a dark-amber or brownish-orange colour, 

 containing deposited feathery crystals of camphor. A drop of the oil 

 smeared on white writing-paper disappeared without leaving any kind of 

 stain. The sp. gr. of the oil is # 940. Exposed to the air it deposits solid 

 camphor, and at 0° F. a portion becomes solid ; the fluid part being drained 

 off, the other part remained solid up to 2S°, but just above this it liquefied. 



