GAS. 



leave it dry and compact. The latter at 

 a heat between 275 and 300 sublimes 

 without being decomposed ; at 320 it 

 becomes fluid, and is partly decomposed, 

 partly sublimed : between 340 and 480 

 it is decomposed rapidly. The fibrous 

 is not decomposed below 400, but a heat 

 above 450 decomposes it ; at 600 a lumi- 

 nous appearance is produced in the retort, 

 and nitric oxide, nitrous oxide, and nitro- 

 gen, mixed in various proportions, are 

 evolved; at 700 or 800 an explosion takes 

 place. It is best to perform the opera- 

 tion over an Argand's lamp, as the heat 

 may thus be brought to the requisite de- 

 gree speedily, and kept from going too 

 far. It should be received over water, 

 and suffered to stand an hour in contact 

 with it, to free it from any nitrate of am- 

 monia that may have been sublimed, as 

 well as from any acid suspended in it. 

 Dr. PfafF recommends mixing very pure 

 sand with the nitrate, to prevent the 

 hazard of explosion; and observes, that 

 it is particularly requisite it should not 

 be contaminated with muriatic acid. One 

 pound of the compact nitrate, yields 4.25 

 cubic feet of gas, and a pound of the 

 fibrous nearly five cubic feet. 



The most singular property of this gas 

 is its action on the animal system. Dr. 

 Priestley had found that it was fatal to 

 animals confined in it. Mr. Davy first 

 ventured to respire it, which he did to 

 considerable extent. When breathed 

 alone for a minute or two, and some have 

 gone so far as four or five minutes, it 

 generally produces a pleasant ttmlling, 

 particularly in the chest and extremities, 

 frequently with an inclination to laugh, 

 and sometimes an irresistible propensity 

 to gesticulation and muscular exertion. 

 The mind meanwhile is often totally ab- 

 stracted from all surrounding objects. 

 Sometimes its effects are not entirely dis- 

 sipated for some hours ; and it is remark- 

 able, that, however strong they may have 

 been, no sense of debility or langour is in- 

 duced after they have subsided. On a few 

 individuals, however, its effects have been 

 unpleasant and depressing; in some it 

 has produced convulsions, and other ner- 

 vous symptoms ; and on some it has bad 

 no sensible effect. Indeed, not only dif- 

 ferent persons, but the same individual, 

 will be variously affected by it, perhaps, 

 at different times. Similar effects have 

 been produced on those who have tried 

 it abroad. 



In debility, arising from residence in a 

 hot climate, and intense application to 



business, this gas has proved a complete 

 remedy. It has given voluntary power 

 over palsied parts while inhaled, and the 

 subsequent application of other remedies 

 has effected a cure. Dr. Pfaff has sug- 

 gested its use in melancholia : but in 

 some cases of this disease it has done no 

 good, and in one harm. 



GAS, nitrogen or azotic. Under the 

 article ATMOSPHERE it has been observ- 

 ed, that about three fourths of our at- 

 mosphere consist of gas, unfit to main- 

 tain combustion, or support life. It is 

 called nitrogen or azotic gas, and is a 

 little lighter than atmospheric air. It is 

 incapable of supporting life, or combus- 

 tion, yet a small portion is absorbed in 

 respiration. It is not inflammable, though 

 it unites with oxygen in different propor- 

 tions, forming nitrous oxide, when the 

 oxygen is only .37, nitric oxide when it 

 is .56, and nitric acid when .705. It is 

 one of the most general elements of ani- 

 mal substances. With hydrogen it forms 

 ammonia ; and Fourcroy suggested, that 

 it might possibly be the alkaligenating 

 principle, though he confesses there are 

 no facts in support of this conjecture ; 

 the name of alkaligen, therefore, which 

 has been proposed for it, is certainly in- 

 admissible. It dissolves small portions of 

 phosphorus, sulphur, and carbon. 



GAS, oxygen. This gas was obtained 

 by Dr. Priestley in 1774, from red oxide 

 of mercury exposed to a burning lens, 

 who observed its distinguishing proper- 

 ties of rendering combustion more vivid, 

 and eminently supporting life. Scheele 

 obtained it in different modes in 1775 ; 

 and in the same year Lavoisier, who had 

 begun, as he says, to suspect the absorp- 

 tion of atmospheric air, or, of a portion of 

 it, in the calcination of metals, expelled 

 it from the red oxide of mercury heated 

 in a retort. Priestley called it dephiogis- 

 ticated air ; Scheele, from its peculiar 

 property, fire air, a name before given it 

 by Mayow, or empyreal air. 



Oxygen gas forms about a fourth of 

 our atmosphere, and its base is very 

 abundant in nature. Water contains .85 

 of it, and it exists in most vegetable 

 and animal products, acids, salts, and 

 oxides. 



This gas may be obtained from nitrate 

 of potash, exposed to a red heat in a 

 coated glass or earthen retort, or in a 

 gun barrel, from a pound of which about 

 1200 cubic inches may be obtained ; but 

 this is liable, particularly towards the end 



