1818.] the Commence?)ient of the Year 1817. Part I. II 



Lussac, which is exactly the specific gravity of one volume of 

 oxygen gas and two volumes of hydrogen gas reduced into l£ 

 volume; for 



Oxygen = = 1*1111 



Hydrogen = -0G94 x 2 = 0*1388 



2 ) 1*2499 



Sp. gr. of steam = 0*6249 



3. Volta's Eudiometer. — The little apparatus known by the 

 name of Volta's eudiometer is indispensable in every laboratory. 

 It is employed in burning mixtures of inflammable gases and 

 oxygen gas by means of an electric spark, in order to determine 

 the quantity of oxygen requisite to consume a given volume of 

 the inflammable gas, and the nature and proportions of the 

 products. The eudiometer universally employed by British 

 chemists for this purpose, is the modification of Volta's eudio- 

 meter contrived by Mr. Pepys. It consists of a very thick glass 

 cylindrical tube shut at one end, about eight inches long, half 

 an inch in diameter, and graduated into inches, tenths, and 

 hundredths. The upper extremity is pierced by two thick brass 

 wires, terminating on the outside by rings, and on the inside by 

 blunt ends. By means of these wires, the electrical spark 

 destined to kindle the gas is passed. It is alwavs left open 

 below. All risk of any loss of gass is avoided, by making the 

 quantity of gas consumed sufficiently small to prevent the 

 expansion from driving out the whole of the water. 



In France it is customary to shut the bottom of the tube by a 

 stopper. This precaution, while it secures the experimenter 

 against any escape of gas, exposes him to another source of 

 error, perhaps still more dangerous than that which the stopper 

 is intended to guard against. After the explosion, a portion of 

 the gas is usually deprived of its elastic form. Hence a partial 

 vacuum is formed in the eudiometer ; and the water contained in 

 the tube of course lets go the air with which it was previously 

 impregnated. I have long suspected that the small quantities 

 of azote which Theodore de Saussure met with in some of his 

 analyses, might possibly have originated in some such way. 

 Gay-Lussac has proposed a very simple and ingenious method 

 of obviating this source of error. To the lower end of the 

 eudiometer he fixes a conical valve, opening inwards. At the 

 moment of the explosion, the valve is pressed down, and prevents 

 any escape of gas. When the vacuum begins to be formed, the 

 water, in which the eudiometer stands, forces up the valve, 

 rushes in, and prevents a vacuum from being formed.— (Ann. de 

 Chim. et Phys. iv. 188.) 



4. Dr. Marshall Hall has contrived a very simple and ingenious 

 instrument to save the practical chemist the trouble of reducing 

 the volumes of the gases on which he is experimenting to a 



