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inflammability, infolubihty m water, and iolu-hi;ity in alcohol, there are fcvcral other cii-cumftances which have ulualiv been employedto didinguifh the dalles of refins.

Balfums according to the antient fenfe of theword was certainly applied limply to thofe refinsthat always remained in a fluid or femin-fluidHate, fuch as the Balfam of Capivi, of Mecca ,of Canada , &c. and thefe appear to be refinsholding a fuperabundance of eflential oil, fo thatwhen diddled per fe a vaft quantity of oil ariles,and a hard brittle refin is left behind if the heatemployed is only moderate. Thus turpentine,which is a natural balfam, yields by didillationabundance of the eflential oil of turpentine ;and common rofin (which is a true refin) is leftbehind.

The term Balfam however has of late beeninjudicioufly applied in the modern chemicalnomenclature to thofe two or three fpecies ofrefins that contain a notable quantity of Benzoicacid, as deferibed under that article.

Gum refins are natural mixtures of a truerefin with another fubdance apparently ofthe nature of gum and foluble in water.Hence if they are triturated with water, theyremain fufpended in it in pretty intimate mix-ture for a confiderable time, forming an opakeemulfive liquor. By Handing, however, therefill fubfides, and the liquor' becomes clear,but it retains the flavour and fmell of the gumrefin, and leaves on evaporation a fmall quantityof brown extractive matter. Gum-ammoniacis an example of this kind. This didinCtionhowever is not very precile, and is more ufefulin pharmacy than in pure chemidry.

There are fome fubdances evidently refinousin their nature and origin, but which haveother peculiar properties that have caufed themto be excluded from the lilt of refins.

Camphor is of this kind, which poffeffcsfome didinftive characters that have alreadybeen fully deferibed under that article.

Caoutchouc , copal, and perhaps amber alfo,appear to belong ItriHly to the clafs of refills,but each has fome points in which it differsmaterially from them.

We {bail refer our readers to the articlesVarnifk and Turpentine for fome of the moltimportant individual refins, and in this placeonly notice fome chemical properties commonto the whole clafs.

All the refins fink in water. Mod: of themare without fade or only give a flight pungencywhen long chewed. When heated per Je in a

* Fourcroy, h Ibid. c Ciil.*!'

clofe veflel, they firft give a confiderable quan-tity of eflential oil proportionate to the foftnefsand approach to liquidity of the refin, afterwhich, if the heat is raifed, they yield an acid-ulous water, carburetted hydrogen, and car-bonic acid, and a brilliant fpongy coal is left.The refins burn readily in the air, with muchflame and a very denfe fmoke, which lattercarries with it a large quantity of very purecharcoal, that fettles upon all the contiguousfurfaces, covering them with a fine lamp-black.Much water is alfo generated during this corn-bullion.

Refins unite by melting, with fulpnur, andalfo with phofphorus though with difficulty.*It is generally afferted that neither alkalies noracids have any a&ion upon refin, neither in-flaming nor oxydating them nor reducing themto a foap., b This however is found to be en-tirely a miflake, for many of the acids, and thefixed alkalies aft very powerfully upon thefefubftances, as has been fhewn by Mr. Hatchettin his .valuable analyfis of gum lac, c and morelately in his experiments on the production ofartificial tannin. d The former have been al-ready mentioned under the article lac : , and thelatter we fhall chiefly refer to tannin, but witha fhort notice in this place of that part of thefehighly curious refearches which more immedi-ately refers to the properties of refins.

Potafh compleatly difTolves refin by longboiling, and carbonat of potafh adds confider-ably upon it though much lefs perfectly. Thisfolution is clear and of a faponaceous confift-ence, and will bear dilution with water withoutbecoming turbid, but on the addition of an acidthe whole of the refin feparates.

If a metallic folution in acid be added to thealkaline folution of the refin, a curdy precipi-tate is formed, confiding of the refill unitedmod intimately with the metallic oxyd, whichbears a drong rcfemblance to the fimilar preci-pitates formed by adding a metallic folution tofoap.

When dvong nitric acid is digeded withrefin it is iird converted into a pale orange-coloured porous brittle fubdance, after whicha repeated abdradtion of the acid at a boilino-heat, converts the refin into a deep yellow vifeidfubdance, foluble both in water and alcohol, intoa clear liquor, in which mod of the refinous pro-perties are loll. Very long continued digedionin the acid without heat will produce the fameeffe£t. Nitrous gas is produced in abundanceduring each didillation, and the drength of the

i-anf. for 1804. * Ditto for 1805 and 6.