1839] 



On Chemical Tests. 



295 



precipitate consists of albumen and protoxide of copper j" the per cent- 

 age of the oxide being about I 65. 



c. Albumen is not precipitated by phosphoric nor by acetic acid. 



d. If water containing ToW of its weight of albumen be boiled, it 

 vnll be rendered perceptibly opaque. This is a distinguishing charac- 

 teristic, and sufficiently delicate for p?actical purposes. 



e. Ferrocyanate of potash is a delicate test also, but a slight excess 

 of acetic acid should be previously added. 



23. ALCOHOL is useful in analysis, and for making tinctures. Its 

 strength is known by its specific gravity, which in the strongest is about 

 0.800. It detects the adulteration of volatile or essential oils with fixed 

 oils, thus; mix a few drops of oil of almon*ls, or of olivrs, with any es- 

 sential oil, say oil of lavender, and pour alcohol on the mixture; the es- 

 sential oil will dissolve in the spirit, but the fixed oil will not. Pour off 

 the alcholic solution, and add thereto distilled water ; the water will 

 unite with the alcohol, and set the essential oil at liberty, which may be 

 thus obtained pure and freed from the adulterated oil. See 73 regarding 

 the action of alcohol with acids, and aethers. 



a. Alcohol dissolves soap, vegetable extract, sugar, oxalic, cam- 

 phoric, tartaric, gallic and benzoic acids, volatile oils, resins, balsams; 

 fixed oils it dissolves but sparingly except castor oil which it dissolves 

 in considerable quantity. It combines with sulphur, phosphorous, and 

 the pure alkalies, but not with their carbonates, nor when pure with any 

 of the earths. Some salts in solution particularly sulphates are preci- 

 pitated on the addition of alcohol ; by this means salts insoluble in al- 

 cohol are sometimes separated in chemical analysis. 



b. When alcohol is set on fire, mingled with boraeie acid, the flame 

 is green; with nitre, common salt, and the salts of barytes the flame is 

 yellow : with strontia, rose-red ; with salts of copper, a greenish hue ; 

 and a red colour with the salts of lime and lithia. 



24. ALKALIES and their carbonates, may be detected bij litmus 

 paper, see 78. Potash is distinguished from soda by the tests, Nos, 

 19.97.110. Alkalies and their carbonates act on almost all the metals, so 

 that they are not discriminative tests, but are useful auxiliaries. See 

 table of re-agent*. 



25. ALUMINA, muriate of, detects carbonate of magnesia in so- 

 lution. If an alkali be present it must first be neutralized. 



26. ALUMINA if pure is white, but is often yellowish and horny 

 when obtained by gently drying the hydrate of alumina. It is insoluble 

 in water, but soluble in acids if it has not been ignited. After ignition 

 it is best dissolved by digestion in concentrated muriatic acid, diluted 



