ALCOHOL.—ALUM.
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distilled water, and carefully drying it at a heat whichmust not exceed 100° Fahr. (37°'7 C.) ; after whichit is weighed. The quantity of mercuric fulminateobtained is nearly equal to that of the alcoholcontained in the wood-spirit; and at any rate, theformation of the detonating salt is quite characteristicof the presence of alcohol, since wood-spirit treatedby nitric acid in the presence of mercury or silverproduces neither fulminate of silver nor fulminate ofmercury.
In applying this test the greatest care should beexercised, and every precaution taken to preventcontact of any hard body with the precipitate, sincethe fulminates of silver and mercury, and especiallythe former, are very explosive; silver fulminate(Ag 2 C 2 N,0 2 ) has been known to explode by contactwith a glass rod, even under water; the mercuricfulminate is less explosive, and is on that accountpreferred. For the purpose of collecting thesecompounds, the feather of a quill should be used;and if the quantity exceeds a few grains, it should becollected in several filters so as to handle only smallportions at a time. During the evolution of theethereal vapours all approach of flame should becarefully avoided.
The same chemist gives the following as theprincipal tests whereby to discern alcohol from woodnaphtha, and also whether the latter is genuine ormixed with alcohol:—
1st. The boiling point of pure wood naphtha spiritis at least 20° Fahr. (5°-5 C.) below that of alcoholof the same density, and it exhales the characteristic,pungent, and offensive odour of aldehyde. In thecourse of his experiments he found the boilingpoint of—
Fahr. C.
Wood-spirit, of specific gravity ’870, to be 144° 62°-2
Alcohol, of like gravity,.180° 8‘2°’2
Wood-spirit, of specific gravity '832,. 140° G0°-0.
Alcohol, of the same density,.171°*1 77°-2
If 10 per cent, of naphtha be mixed with alcohol, theboiling point is lowered at least 6° Fahr. (3°-3 C.)
2nd. When rectified naphtha is distilled at thetemperature of boiling water from a largo quantityof lime, the distillate is unchanged in its gravity,whilst if alcohol, or a mixture of alcohol and naphtha,be subjected to the same treatment, the first portionsthat come over are nearly absolute, .and stand ata density below - 800, and contain, at 60° Fahr.(15°-5 C.), about 70 per cent, over proof. Thereason of this characteristic difference seems to bethat naphtha possesses a stronger affinity for waterthan alcohol.
3rd. When water is added to alcohol, the specificgravity of the liquor becomes reduced in a less pro-portion than when wood-spirit of the same gravityas the alcohol is diluted with the same quantity ofwater. Thus, for example, if alcohol of a givendensity is diluted with a certain quantity of water,so as to bring it to specific gravity 0-920, wood-spiritof the same original gravity, and diluted with thesame quantity of water, will become of specific gravity0-926 or 0-927.
When brandies, gins, and other alcoholic liquorsvol. r.
arc artificially made by admixture of various ingredi-ents with alcohol, as is directed under these heads,it is not uncommon to find that the alcohol, in suchcompounded articles, is attenuated as low as possible,and that the agreeableness of taste and the pungencyof flavour peculiar to the genuine beverages, areconferred upon the mixture by means of pepper,cayenne, or other acrid substances. These sophisti-cations are discovered by evaporating a knownquantity of the liquid to dryness at a gentle heat,when the added substances will be found as a residue.
Acetates of copper and lead are rarely found inbrandies, owing to the repeated distillations to whichthe spirit is subjected, but when the old stills areemployed, the solder connecting the seams of thestill is apt to be dissolved by the small quantity ofacetic acid present in the liquors; plumbic acetate(sugar of lead) has likewise been known to be added tofacilitate the clarifying process. Liquors thus treatedare extremely pernicious, since the acetates of leadare highly poisonous. By filtering the brandy throughanimal charcoal, and adding sulphuric acid to theclear liquor, if the lead is present in excess a whiteprecipitate appears; if there is no precipitate, astream of sulphuretted hydrogen is to be transmittedthrough the liquid, and if any lead is present, a blackprecipitate or coloration is produced. Should awhite precipitate be obtained by the action of sul-phuric acid or sodium sulphate on the brandy, it isturned black by the addition of ammonium sulphide;and if the precipitate should bo bulky it may bemixed with a little sodium carbonate, and reducedon charcoal before the blowpipe to a globule of metal.
Copper may be detected by filtering a portion ofthe brandy through animal charcoal, to decolorize it;ammonia is then added to the clear liquor, to whichit will impart a blue tinge, if copper be present insufficient quantity. Several hours are sometimesrequisite to determine this appearance. The presenceof copper may also be detected by immersing a bladeof perfectly clean iron in the brandy, and leaving itthere for a few hours, when it will be found coatedwith a film of metallic copper. The brandy, firstdecolorized by animal charcoal, may also be testedfor copper by a solution of potassium ferrocyanide,which will produce a reddish brown precipitate withthis metal.
ALUM.— A/un, French ; alaun, German ; alumen,Latin . According to Beckman alum was first dis-covered in Asia , and was certainly not known to theGreeks or Romans, what the latter called alumenbeing green vitriol (ferrous sulphate). The Greeksand Romans mention only natural alum; now alumis very rarely produced spontaneously, and then onlyas an efflorescence on stones in the neighbourhoodof certain mineral waters. Crystals of alum are alsooccasionally found upon minerals containing muchaluminium when they have been long exposed to theweather; but even then they are so small and somuch scattered as to require close observation todiscover them. The celebrity acquired by alumenamong the ancients, as a substance extremely usefulin dyeing and medicine, was entirely forgotten at the
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