290 PROFESSOR LETTS ON PHOSPHORUS-BETAINES. 
affinity for carbon ; for although, undoubtedly, bisulphide of carbon is obtained 
with greater ease than cyanogen—the compound ammonias (bodies in which 
carbon is directly united to nitrogen)—are so numerous, stable, and so easily 
obtained, that we must accord to nitrogen a very high degree of affinity for 
carbon. Phosphorus, on the other hand, has but a slight attraction for carbon. 
The two elements do not combine directly (so far as we know) to form a com- 
pound analogous to cyanogen, and even the compounds which phosphorus forms 
with hydrocarbon radicals (phosphines) are only obtained with difficulty. 
This striking difference between the three elements explains, in the 
author’s opinion (in some measure at least), the curious fact, that whereas both 
nitric and sulphuric acid readily act on a large number of aromatic bodies in 
such a manner that the nitrogen or sulphur becomes directly united to the 
carbon which they contain, phosphoric acid or anhydride is without action on 
them. Considering the analogies which certainly exist, and are always insisted 
upon, between nitrogen and phosphorus, and also those which exist (but 
are not so commonly insisted upon) between sulphur and phosphorus—we 
should certainly be strongly inclined to predict, if we did not know to the 
contrary, that ‘ phospho” bodies ought to be easily produced by the action of 
phosphoric acid or anhydride on aromatic hydrocarbons. It is almost unneces- 
sary to say that these bodies are known. We are acquainted with phosphinic 
and phosphonic acids (R’PO(OH), and R’,PO(OH)), and with phosphine 
oxides (R;PO), substances which are strictly analogous to sulphonic acids 
(RSO,(OH)) and sulphones (R,SO,), and which are produced by a similar pro- 
cess, viz., by the oxidation of phosphines, but their preparation from phosphoric 
acid or phosphoric anhydride cannot be accomplished. 
Organic Compounds of the three Elements.—Nitrogen is remarkable for 
the ease with which it combines with carbon partly saturated with other 
elements, and consequently the number of organic compounds containing 
- nitrogen is very large. The number of these is increased by the fact that 
nitrogen easily combines not only with hydrocarbon radicals, but also with 
radicals containing carbon, hydrogen, and oxygen. Thus the amides are among 
the most numerous of the organic compounds of nitrogen. 
Compounds of sulphur and hydrocarbons are readily obtained, and the mer- 
captans (compounds which may be considered as analogous to primary or 
secondary amines) are also numerous. But compounds of sulphur with 
oxidised organic radicals are scarce. However, we know of thi-acetic acid 
((CH,—CO)SH) and sulphide of acetyle ((CH,—CO).S), which may be con- 
sidered as analogous to primary (or secondary) and tertiary amides respectively. 
Primary, secondary, and tertiary phosphines are known, and are analogous 
in composition and in many of their properties to amines, but the author is not 
