356 Dr Marcet’s Experiments on Sea-Water, 
name Porphyry, or purple, applied to this stone, was taken from 
the ancient purple dye, made of the shell-fish called Porphy- 
ries, which was got near Tyre. It is, therefore, supposed that 
the ancient dye was of the dull red colour, which this stone ex- 
hibits. A small grained greenish porphyry is sometimes found, 
but much more rarely than the red porphyry, amongst the re- 
mains of ancient art at Rome ; it is quite different from the an- 
tique green serpentine. 
Antique Serpentine. — The green antique serpentine, which 
occurs in pavement of churches at Rome, is one of that class of 
stones called porphyry by the mineralogists. 
Verde di Corsica. — In the Vatican there is a vase, which is 
probably antique, formed of the rock compounded of jade and 
sehillerspar. This rock occurs near the magnesian serpentine in 
Tuscany and in Corsica. 
Egyptian Breccia. — The Egyptian Breccia, which occurs in 
some monuments at Rome, is a conglomerate, composed of hard 
siliceous stones. 
Art. XXVII. — Abstract of Experiments on the Specific Gra- 
vity., Temperature, and Saline Contents of Sea-Water,^ 
By Alexander Marcet, M. D. F. R. S., &c 
I HE very interesting paper of which we propose at present to 
give a brief analysis, is the production of an individual no less 
celebrated by his talents as a chemist and a physician, than by 
those better qualities, without which the loftiest attainments 
lose their splendour and their influence. During the last twen- 
ty years, a period during which England has contributed more 
than her usual contingent to the advancement of science. Dr 
Marcefs exertions have frequently held an honourable and 
conspicuous place ; and we regret to think, that England is so 
soon to lose the benefit of his co-operation, as well as the in- 
fluence of his example. 
Dr Marcet’s attention was directed at an early period to the 
analysis of water, and when the late celebrated Mr Tennant 
received from Sir Joseph Banks, some phials of the water of 
the Dead Sea and of the River Jordan, brought home bv 
* See Phil. Trails. 1819, part ii. p. 161. 
