PROFESSOR LETTS ON PHOSPHORUS-BETAINES. 287 
phosphines ; and even partly oxidised compounds of phosphorus often greedily 
absorb oxygen, and are, as a consequence, powerful reducing agents. 
Similar compounds of sulphur do not as a rule oxidise spontaneously, or if 
they do so the oxidation occurs slowly, as with solutions of sulphuretted hydro- 
gen and metallic sulphides. But oxidising agents easily attack them and 
convert them into oxidised products. Thus sulphuretted hydrogen, by simple 
contact with sulphuric acid, is oxidised to water and sulphur. Organic sul- 
phides (R’,S) are converted by treatment with nitric acid into sulphanes (R’,SO), 
and sulphones (R’,SO,) ; mercaptans (R’HS) into sulphonic acids (R/HSO.). 
Corresponding compounds of nitrogen show much less tendency to oxidise, 
and only in a very few cases are they capable of directly fixing oxygen ; thus 
in the case of the compound ammonias although oxidised products are known 
(R’NO, R’NO,, &c.) they are not produced by direct oxidation. 
These considerations help us to understand the action of reducing agents 
on oxidised compounds of the three elements, and also explain why completely 
different methods must be employed for obtaining their organic compounds. 
A nitro-body is an oxidised compound of nitrogen; in it the oxygen is only 
weakly held, consequently a reducing agent easily removes it, and usually 
causes the addition of hydrogen.* Consequently an amine is readily obtained 
by the reduction of a nitro-body. Oxidised compounds of sulphur are also 
easily reduced. Thus nascent hydrogen de-oxidises sulphuric,.sulphurous, and 
hyposulphurous acids, and converts them into sulphuretted hydrogen, and is 
also capable of converting (certain at least of the) sulphanes and sulphones 
into sulphides. But it is more difficult to reduce an oxidised sulphur com- 
pound than an oxidised nitrogen compound. For instance, nitrate of potash 
is easily reduced to nitrite, and eventually to oxide of potassium by heat alone ; 
whereas sulphate of potassium suffers no change when heated unless a reducing 
agent such as carbon is present ; in which case, however, the oxygen is removed. 
But if we attempt to remove oxygen from an oxidised compound of phos- 
phorus by ordinary reducing agents, we experience as a rule much greater 
difficulty. It is stated that both phosphorous and hypophosphorous acids may 
be reduced by nascent hydrogen,t but phosphoric acid is not affected by that 
reagent, nor is the oxide of a tertiary phosphine. A powerful reducing agent 
acting at a high temperature must generally be employed for the reduction 
of an oxidised compound of phosphorus. 
We can therefore readily understand why phosphines cannot be prepared 
by the reduction of oxidised organic compounds of phosphorus, whilst amines 
are produced by such a process with the greatest ease, and even sulphides are 
formed from sulphines, sulphones, &c., without much difficulty. 
* Not however in all cases, as we see in the preparation of azo-bodies. 
+ This statement requires confirmation. 
