Congelalion of Volatile Oils, 183 



ethers, on the contrary, preferve their fluidity at a much lower term. It is upon thefe laft 

 chiefly that I have direfted the operation of cold, with two obje£ts of refearch : the firft, 

 to obferve the cryftallizatlon which thefe oils might exhibit by the lofs of their caloric ; 

 the fecdnd, to afcertain the other phenomena which might arife during the experiments. 



Thefe experiments, though apparently fimple, are not however without their difficulties. 



When we refle£l on the different chara£lers of volatile oils, we find in general, that the 

 oils obtained from the plants of hot climates are heavier and lefs limpid than thofe of 

 colder regions, and that they contain a fait capable of cryftallization ; that the oils extra£led 

 from the fame plants of our climates vary in colour and fluidity, according to the nature 

 of the foil in which the plants have vegetated, the care in culiivation,the influence of light, 

 the different dates of growth, and whether they be recent or dry when fubje£led to diltil- 

 lation : that when extra£led from the vegetable, they are expofed by the nature of their 

 principles to different alterations, according to the more or lefs effe£lual aftion of the air, 

 the contaiH: of light, whether kept Ln bottles entirely or only in part filled, or clofed with 

 a ground flopper or with a cork. Thefe differences will eafily fhew that the refults muft be 

 fubje£t: to variation : and I have accordingly been very careful to ufe only fuch volatile oils 

 as were newly extradled from frefli vegetables ; with the exception of thofe from exotic- 

 plaiits» 



Concerning the ABion of Cold on fever al Volatile Oils. 



I HALF fjJled feveral very thin bottles with the volatile oils of peppermint, orange 

 flowers, lemon-peel, bergamot, buds of lavender and of thyme, being plants of our cli-- 

 mates ; oil of turpentine, a refinous fubflance, and oil of cinnamon, a foreign bark. , 



Thefe bottles, clofed with ground floppers, were expofed for feveral days on a terrace 

 where a mercurial thermometer marked 1 1° beneath the freezing point (7° Fahrenheit). 



At this degree of cold I obferved that there was formed at the upper internal part of the 

 bottles a ctyftallization in different ramifications, fimilar to thofe feen on the windows of 

 apartments in very cold weather. 



Oil of bergamot exhibited a number of fmall elliptical laminae in its fubftance ; that of 

 lemons had depofited fmall cryftals j oil of orange-flowers exhibited a diminllhed fluidity ; 

 that of cinnamon was partly congealed on the augmentation of the cold, when the thermo- 

 meter in my laboratory ftood at 15° below freezing ( — i" Fahrenhei*). I took advantage 

 of this time to expofe the fame oils to the a£lion of an artificial cold, which I procured by 

 a mixture of ammoniacal muriate and ice, which caufed the thermometer to fink to 22 de« 

 grees ( — i'"^ Fahrenheit). I kept up the fame degree of cold for two hours, by alternately 

 adding the ammoniacal muriate and ice. During the adlion of this cold upon the oils, the 

 ftoppcrs were raifed by the expanfion and difengagemcnt of a gafcous fubftance, which per- 

 fumed the laboratory .and its environs more flrongly than when thefe oils were diftilled in 

 fummer. The upper part of the bottles was lined with needles, of which the ramifications 

 formed dendrites. When the furrounding ice began to change its temperature, 1 proceeded 

 to examine the oils as fpeedily as poflTible, and remarked : 



1. 'I he interior furface of the bottle which contained the oil of peppermint was covered 



with fmall needles which formed a capillary vegetation. They were white, and liquefied on 



the fingers. 'When applied to the tongue, they allbrdfd the frtfli and pungent fmtll of the 



S oil. 



