184 SCIENTIFIC AMUSEMENTS. 



matter of animal or vegetable origin in closed vessels so arranged 

 that the substance is not burnt by access of air, but is decomposed 

 or broken up under the influence of heat, such products as are 

 liquid at the ordinary temperature being condensed by suitably 

 cooling the gases and vapour evolved ; thus in the last experiment, 

 coal was destructively distilled in the retort. 



For coal substitute chips of wood \ it will now be found that a 

 large quantity of permanent gas is produced, which, like coal gas, 

 will burn with a more or less luminous flame ; besides this a 

 variety of tar will condense and an aqueous liquor which, with 

 most kinds of wood, will exhibit an acid and not an alkaline 

 reaction, i.e., it will turn blue litmus paper red, and not vice versa. 

 The acid thus produced is in consequence ieimedipyroligneous, i.e., 

 produced from wood by heat ; it mostly consists of acetic acid, the 

 acid of vinegar (Expt. 193). Besides this acid, the watery fluid 

 also contains an ill-smelling spirituous substance termed wood spirit 

 (pyroligneous spirit or pyroxylic spirit) this spirituous fluid is 

 extracted and mixed with pure alcohol to render it undrinkable, 

 the "methylated spirit" (Expt. 40) thus produced being still 

 capable of use for. burning , varnish-making, and such like purposes. 



Expt. 202. Destructive Distillation of Bones. Substitute 

 bones or gristle for wood in the previous experiment. A very 

 foul-smelling tar will be obtained, and a strongly alkaline watery 

 fluid, much ammonia being produced during the destructive distil- 

 lation of animal substances. For this reason the alchemists 

 termed ammonia the volatile alkali (compare Expt. 143), whilst 

 the name spirit of liartslwrn, sometimes applied to solution of 

 ammonia, is also derived from the fact that ammonia is produced 

 by heating horn. The coke left in the retort when the distillation 

 of bones is complete is known by the name of bone charcoal or 

 bone black, and is largely used as a means of decolorising syrups in 

 sugar refining (Expt. 289), on account of its remarkable power of 

 attracting certain substances into its body and thus removing them 

 from solution. Charcoal from dried blood is still more energetic 

 in this way. 



Expt. 203. Action of Lime and Caustic Soda on Nitrogenous 

 Matter. Many substances are known which contain as one of 

 their constituents the element nitrogen ; most of these possess the 

 property of forming ammonia (a compound of nitrogen and hydro- 

 gen) when they are heated with slaked lime, or powdered caustic 

 soda, or with a mixture of the two (soda-lime). 



Heat in a dry test-tube a few grains of uric acid (the chief 

 constituent of the sediment forming in many kinds of urine on 

 standing) previously mixed with two or three times its bulk of 



