49 o SCIENCE PROGRESS 



affinity is met with either in the case of hydrogen chloride or 

 in that of ammonia ; but although these have no tendency to 

 fall victims to self-loves their affection for water is extra- 

 ordinary, the former being soluble to the extent of nearly 500 

 volumes and the latter to the extent of about 1,100 volumes in 

 one volume of cold water. A solution of hydrogen chloride 

 saturated at o° contains about 82 parts of the chloride to 100 

 of water, corresponding to the ratio HC1:2-40H 2 . A solution 

 of ammonia saturated at o° contains about 87 parts of the 

 nitride per 100 of water, corresponding to the ratio NH 3 : riOH 2 . 

 Hydrogen oxide also, it may be pointed out, is undoubtedly 

 soluble in water at all temperatures; but it is impossible to 

 measure its solubility. 



Still more striking proof of the unsaturated nature of hydro- 

 gen chloride and nitride is afforded by the manner in which 

 these two gases at once interact when brought into contact, 

 forming solid ammonium chloride, NH 4 C1, a well-defined 

 crystalline substance. 



Whilst, therefore, a single atom of carbon combines with 

 four atoms of hydrogen and these four atoms of hydrogen 

 satisfy it and are satisfied by it practically entirely, no one of 

 the other three elements considered is satisfied by the number 

 of hydrogen atoms with which it can combine — in other words, 

 chlorine, oxygen and nitrogen in contradistinction to carbon 

 are all possessed of a greater atom-fixing power, a higher 

 valency, than is indicated by their affinity for hydrogen. 



But this higher or extra valency is a function of a different 

 order from the normal or hydride valency, as it may be termed : 

 the latter being a fixed the former a variable and dependent 

 function. 



Thus if the hydrogen in hydrogen chloride be displaced by 

 the hydrocarbon radicle methyl, CH 3 , a neutral and practically 

 inert substance, methyl chloride, CH 3 C1, is produced. In like 

 manner both methyl alcohol and methyl ether, CH 3 .OH and 

 CH 3 . O . CH 3 , are not only far less active substances than water 

 is, but their boiling points are considerably lower than that of 

 water, the alcohol boiling at 66°, the ether being a gas although 

 of higher molecular weight than the alcohol. If methyl be 

 substituted for hydrogen in ammonia, however, it has little 

 influence on the nitrogen in depriving it of its power of 

 attracting acids; the solubility in water of the amine (CH 3 ) 3 N, 



