181. Mr. Stenhouse's Analysis of 



of settling the question by extending the levels as above stated, 

 I need not say more, but leave the question to be decided, as 

 I hope it soon will be, by such extension of the levels. 



I do not mean to dispute Mr. Whewell's theory as to the 

 mean levels of the tides, supposing there were no obstructions 

 to their free action ; but I do conceive that it is very possible 

 that circumstances may operate to prevent the mean level of 

 the tides from being at the same elevation at every part of the 

 coast. 



My object is to prevent any general conclusion with respect 

 to tide-levels from being acted on until the fict be placed be- 

 yond doubt; and whatever may be the result of the inquiry, 

 the levels which may be determined will be available for esta- 

 blishing the elevations of certain fixed points or beiich-marks, 

 which will always be much more useful for reference than any 

 determination depending on the tides. 



Falmouth, Jan. 4, 1841. 



M' 



XXXV. Analysis of the Oils of FAemi and Olihajmm. 

 By John Stenhouse, Esq.* 

 OST of the resins contain, as is well known, volatile oils, 

 to which they owe their peculiar odours. A considerable 

 number of these oils have been carefully examined, but there 

 are several, and among the rest those of elemi and olibanum, 

 which, as far as I am aware, have not previously been sub- 

 jected to analysis. 



I was induced therefore to prepare a quantity of each of 

 them for this purpose. 



Elemi Oil. — Prejjaraiion. A quantity of pulverized elemi 

 resin was distilled with water in the usual way. The larger 

 portion of the oil came over at an early period of the distilla- 

 tion, and collected on the surface of the water in the receiver, 

 from which it was easily separated by means of a sucker. It 

 was then allowed to remain some days over fused chloride of 

 calcium to render it anhydrous, and afterwards rectified. It 

 is stated in most systems of chemistry, on the authority of 

 Bonastre, that elemi resin yields 11^ per cent, of volatile oil, 

 but though I operated on an apparently fresh and unadulter- 

 ated specimen, I did not succeed in obtaining more than 3i 

 per cent. 



Properties. — Elemi oil is a transparent colourless liquid of 

 an an-reeable smell, similar to that of the resin, and of a pun- 

 gent taste. Its specific gravity is 0-852 at +24° C. It boils 

 at 140° C. It burns with a bright smoky flame, like oil of 

 * Coniiniinicated by the Author. 



