PROFESSOR LETTS ON PHOSPHORUS-BETAINES. 289 
acids. Their salts are stable at a high temperature, and in a great many cases 
their solubility is similar. 
Nitric acid cannot be said to resemble either sulphuric or phosphoric acid, 
nor can its salts be compared with sulphates or phosphates. 
There is a distinct analogy between hypophosphorous and hydrosulphurous 
acids, and between phosphorous and sulphurous acids. The first two are 
extremely powerful reducing agents, and to the best of the author’s belief they 
are the only substances which precipitate cuprous hydride from a solution of 
a copper salt. Sulphurous and phosphorous acids are also reducing agents, 
but by no means such powerful ones. 
It is rather curious that in this series of acids, so far as their formule are 
concerned, the only difference between corresponding terms is that all the 
members of the sulphur series contain two atoms of hydrogen, whilst those 
of the phosphorus series contain three. 
H,SO, H,PO, 
H,S0, H,PO, 
H,SO, H,PO, 
There is one point in which sulphur does not resemble either phosphorus or 
nitrogen, viz., in the large number of oxy-acids which it forms. No oxy-acids 
of phosphorus or nitrogen have been obtained corresponding with hyposul- 
phurous acid or with the polythionic acids. 
Phosphorus and sulphur also agree in their strong affinity for the halogens, 
especially for chlorine, whilst nitrogen has almost no attraction for them. The 
chlorides of sulphur and of phosphorus resemble each other in certain of their 
properties. ‘Thus the higher chlorides of both readily dissociate into chlorine 
and the lower chlorides, and this is especially the case with the chloride of 
sulphur, SCl, which dissociates even at ordinary temperature into SCl,, or 
SCI, and free chlorine. Again, these higher chlorides act upon the hydrates 
of organic radicals, giving their oxychlorides, chloride of the organic radical, and 
hydrochloric acid. 
The two following equations will illustrate this— 
C,H,—-COOH + SCl, = HCl + SOCl, + C,H,—COCl 
C,H,—COOH + PCl, = HCl + POCI; + C,H,—COCl 
The lower chloride of sulphur is decomposed by water, with formation of 
hydrochloric and sulphurous acids (and free sulphur) ; and the lower chloride of 
phosphorus is decomposed in a similar manner, with formation of hydrochloric 
and phosphorous acids. 
There is a very striking difference between the three elements in their affinity 
for carbon—a difference that explains several facts which at first sight appear 
anomalous. It is difficult to say whether nitrogen or sulphur has the strongest 
