Anatomical Description of the Fir Tree. 259 



tn ma]\ing pitch from tar by inspissation after it has been im- 

 ported into this country, the first product that distils over is a 

 brown, acid water, mixed with a good deal of oil. As the pro- 

 cess proceeds, and the heat is increased, the acid diminishes, and 

 the oil increases. According to Aikin, from GOO gallons of tar, 

 or IS or 20 barrels, the jjroduct will be about 10 barrels of pitch, 

 or 22 cwt., 17 Ggallons of oil, and about 40 gallons of acid. 

 The oil and water, which are distilled over, do not again mix, 

 so that they can easily be separated by decantation. 



Where the temperature, when this tree is planted, is raised 

 above a certain degree, the equilibrium of the compound is de- 

 stroyed ; and the oil, being the most volatile of any of the vege- 

 table oils, flies off in the shape of vapour. The resinous sub- 

 stance at this time, being much heated, becomes more fluid ; and 

 the air being expanded through the whole exterior texture of 

 the plant, the juice is pressed upward by the same means and 

 force as in other plants. Though the assistance of the leaves is 

 comparatively trifling, their deficiency is supplied by the very ex- 

 pansive quality of the juice : a quality it possesses to such a de- 

 gree, that in barrelling tar at Archangel, it is found necessary, 

 to leave a considerable space in the top of the barrel empty; I 

 have been told as much as four or five inches, in order to meet 

 the expansion of our temperature. 



When by a high temperature the juice of the tree, or rather 

 the oil, is forced off in various wavs,as at any amputated branch 

 or wound in the tree, by the buds and leaves, t\;c. ; on the return 

 of the evening, the resinous matter congeals, and fixes itself in 

 the situation where it happens to be, with a very little decline 

 of the temperature ; and becomes almost incapable of being 

 raised any higher by the power of capillary attraction. In con- 

 .sequence of the oily substance being driven off by the heat of 

 the day, and the vessels becoming comparatively emptv, thev are 

 then compelled to absorb more than an ordinary ])ortion of the 

 circumambient atmosphere, not onlv to restore the mccus com- 

 munis, that the tree had perspired in the heat of the day like- 

 other plants, but likewise to fill up the space before occupied by 

 the volatile oil of the sticcus propriiis. 



Thus the fir tree in a warm climate is not oidy liable to be de- 

 prived of its native juices, by one part, which appears to be about 

 twenty-five per cent, of the whole juice, being driven off 'in oily 

 vapour, and another rendered thicli and pitchy, so that it is in- 

 capable of being acted upon any more in the shape of sap ; but 

 likewise to be loaded with matter, to fill the space before oc- 

 cupied by the volatile oil now dissipated. This coming in sonae 

 measure into contact with the resinous substance by the return- 

 ing heat of iuiother day, extracts from it sometlung like the film, 



K 2 thiit 



