40S Mr. WiUiam Bate Hardy [April 6, 



to-day owes his emancipation to the chemical discovery that the 

 properties of a complex snbstance are defined not so much by the 

 kind of atoms or number of atoms of which it is built, as by the 

 arrangement of those atoms in space. 



Here is a simple and startling case. The molecules of two 

 chemical substances, benzonitrile and phenylisocyanide, are composed 

 of seven atoms of carbon, live of hydrogen, and one of nitrogen : 



N C 



There is a small difference in the arrangement of these atoms which 

 is illustrated by the diagram. Now, what are the properties of these 

 two substances ? They are as unlike as possible. The first is a 

 harmless fluid with an aromatic smell of bitter almonds. The 

 second is very poisonous and offensive. 



K vivid impression in regard to the odour of the isocyanides may 

 be produced by the following experiment. In a test-tube bring 

 together a little chloroform, aniline, and alcoholic potash. The 

 reaction takes place at once. " It is better to jierform the e,rperime?it 

 out of doors and in such a place that the tube ivith its contents can be 

 thrown away without molesting any one."" 



In the building of a complex molecule one .has atoms gathered 

 together to form groups, these to form larger groups, and the whole 

 structure is arranged on a fundamental plan or style, like, for instance, 

 the ring of carbon atoms in the two substances just mentioned. 

 There is, therefore, a molecular architecture, and, as in ordinary 

 architecture, there are differences of style and of general plan, Gothic, 

 Norman, etc., with endless variety in detail. Amongst the recognised 

 styles of molecular architecture is the proteid style, and the qualities 

 common to all forms of life are based ultimately upon the esseutinl 

 features of that style, while the differences between one kind of 

 living matter and another are the expression of the differences in 

 detail — the omission of this group, the addition of that. 



Some of the atomic groups which find a place in tlie proteid 

 molecule are readily recognisable by chemical tests — one of these 

 groups occurs as a separate chemical substance called Tryptophane. 

 It shows a vivid purple colour with sulphuric acid and reduced oxalic 



