80 NON-METALS AND THEIR COMBINATIONS. 



inverted into a porcelain dish partly filled with water. Weigh of metallic 

 zinc 0.04 gramme, and bring it quickly under the mouth of the test-tube, so 

 that the generated hydrogen rises in the tube. Prepare a second tube in the 

 same manner, and introduce 0.04 gramme of metallic magnesium. In case the 

 decomposition of the acids by the metals should proceed too slowly, a little 

 more acid may be poured into the dishes. 



When the metals are completely dissolved it will be seen that the volumes 

 of hydrogen in the two tubes bear a relation to each other of about 10 to 27. 



In order to measure the gas volumes as correctly as the simple apparatus 

 permits, the tubes should be transferred to a large beaker filled with cold water, 

 bringing the surfaces of the liquids in the test-tube and beaker on a level, and 

 marking on the outside of the test-tubes (with a file or paper strip) the exact 

 height of the gas. 



After having emptied the test-tubes, they may be filled with water from a 

 pipette or from a burette to the point which has been marked, and thus the 

 exact volume of gas generated is ascertained. 



Repeat the operation, using 0.065 gramme of zinc and 0.024 gramme of mag- 

 nesium. Notice that in this case equal volumes of hydrogen are obtained. 

 Calculate the weight of hydrogen from the cubic centimetres liberated, and 

 compare this weight with the weights of zinc and magnesium used. What 

 relation is there between the weights of the liberated hydrogen and the metals 

 used, and the atomic weights of these three elements ? 



Properties. Hydrogen is a colorless, inodorous, tasteless gas ; it 

 is the lightest of all known substances, having a specific gravity of 

 0.0692 as compared with atmospheric air (= 1). One litre of hydro- 

 gen at C. (32 F.), and a barometric pressure of 760 ram., weighs 

 0.0896 gramme, or one gramme occupies a space of 11.163 litres; 

 100 cubic inches weigh about 2.265 grains. 



Hydrogen resists liquefaction more than any other gas. When 

 subjected to a pressure of 650 atmospheres and a temperature of 

 150 C. (238 F.), hydrogen forms a steel-blue liquid, a portion 

 of which is converted into a solid on suddenly releasing the pressure, 

 in consequence of the intense cold produced by the rapid evapori- 

 zation of the liquefied hydrogen. 



In its chemical properties, hydrogen resembles the metals more than 

 the non-metals ; it burns easily in atmospheric air, or in pure oxygen, 

 with a non-luminous, colorless, or slightly bluish flame producing 

 during this process of combustion a higher temperature than can be 

 obtained by the combustion of an equal weight of any other substance. 



H 2 + O = H 2 0. 



The formation of water by the combustion of hydrogen distinguishes 

 it from other gases. 



Two volumes of hydrogen combine with one volume of oxygen, 

 forming two volumes of gaseous water. 



