410 
Proceedings of the Royal Society 
It is thus shown which of the atoms of hydrogen in propionic acid 
Keplacing CHg in these formulae by CgH- we get the formulae of 
the corresponding substances in the aromatic series. 
The complete analogy between lactic and mandelic acids as to 
the mode of their formation naturally suggests the idea that their 
decompositions should also be analogous ; and yet, considering that 
no oxyacid of the aromatic series had as yet been directly reduced 
to the corresponding normal acid, it seemed to me to he of interest 
to examine the reaction of hydriodic acid on mandelic acid, in order 
to see whether it follows the analogy of salicylic or of lactic acid, 
and if the latter, to compare the toluic acid thus produced with the 
two isomeric acids at present known. 
For this purpose, mandelic acid was boiled with concentrated 
aqueous hydriodic acid and phosphorus in a flask fltted to an 
ascending Liebig’s condenser, so that the vapours of hydriodic acid 
condensed, and ran hack into the flask. Notwithstanding the pre- 
sence of excess of phosphorus, the liquid immediately became 
opaque from the separation of a large quantity of free iodine, and 
the drops of condensed hydriodic acid became milky. After boiling 
for about half an hour, the reaction was complete, and the iodine 
was removed by the phosphorus. The clear liquid, while still hot, 
was decanted from the excess of phosphorus, and on cooling solidi- 
fied to a crystalline magma. The crystals, when drained and re- 
crystallised once or twice from boiling water, presented the follow- 
ing properties ; — 
Large extremely thin iridescent plates, closely resembling those 
of benzoic acid, but without the serrated character of the latter ; 
readily soluble in hot, sparingly in cold water ; readily soluble in 
alcohol, ether, and solutions of the hydrates and carbonates of the 
alkalies. When treated with boiling water, they at first fuse to a 
colourless oil denser than water, and subsequently dissolve, and 
when a hot saturated solution is cooled, the substance is at first 
deposited in the liquid state. 
CH 
is replaced by the water residue HO to form common 
lactic acid, and the latter is distinguished from sarcolactic acid 
