QQ eee se ,hCl,””:—t—“‘_ ao” 
TRANSACTIONS OF THE SECTIONS. 43 
tions of meta-chemistry, which is subject to the dominion of the principle of polarity, 
and includes eleven distinct types, and of para-chemistry, which is subject to the 
principle of parality, and includes three distinct types or forms of molecular group- 
ing. After giving a general description of these various types, the author discusses the 
law of volume-harmony, according to which the volumes of the constituent members 
of a given volume-harmonious molecule are always reducible to some simple ratio 
contained in the volume-harmonious scale: 1:m x1; 1:mx2;2:mx3;3:mx4; 
4:mx5; 5:mxX6; 6:mxX7, where m represents some integral number. The 
volume-harmonious molecules are divided into two classes. The first class com- 
prises all those compounds where the water of crystallization is excluded, and the 
second class all those compounds where the water of crystallization is present. As 
regards the latter class, it is a characteristic peculiarity that in the process of 
reduction the saline molecule, with every fresh addition of one molecule of water of 
crystallization, experiences a loss in volume amounting always to a constant quan- 
tity. This quantity remains unaltered so long as this loss in volume is caused by 
the successive paralysation of its envelope-molecules; but when this process of 
reduction extends to the molecules of the nucleus, the constant quantity in some 
cases continues the same, but in geneftl if merges into another constant quantity. 
Further details, in particular as regards the various conditions and rules intended 
to guide the student in the volume-analysis of the molecules belonging to the para- 
chemical system, are contained in the original paper. 
Analysis of the Roman Mortar of Burgh Castle, Suffolk. 
By Joun Sprrtizr, F.C.S. 
The samples of ancient Roman mortar which form the subject of this memoir, 
were detached for the purpose of analysis in the years 1863 and 1866. They all 
had the reddish colour (due to the admixture of pounded brick) which is con- 
sidered to be characteristic of a Roman origin. The details of construction, dimen- 
sions, and other particulars relating to Burgh Castle, the Gartanonum of the 
Romans, were briefly described, and a water-colour sketch of the castrwm exhi- 
bited: The walls, which are of rubble masonry and about six feet in thickness, 
are faced with flints and triple layers of red tiles, set with great regularity, 
Adopting Mr. C. Roach Smith’s opinion respecting the antiquity of the cas- 
trum, the chemical problem resolved itself into a study of the following leading 
points in reference to the hardening of the mortar, and changes occurring during 
a period of about fifteen centuries, viz. :— 
og To what extent the hydrate of lime becomes recarbonated by exposure to 
air 
2nd. What is the physical condition of the carbonate so produced ? and 
srd. Whether in this long interval the silica and lime can directly unite with 
each other ? 
The conclusion to which the author was led by the chemical examination 
of the ancient mortars from Burgh, Pevensey, and other Roman castra, is that the 
lime and carbonic acid are invariably united in monatomic proportions as in the 
original limestone rock, and that there is no eviderice of the hydrate of lime 
haying at any time exerted a power of corroding the surfaces of sand, flint, pebbles, 
or even of burnt clay, with which it must have been for lengthened periods in 
contact. Further, that the water originally combined with the lime has been 
entirely eliminated during this process of recarbonation, and, this stage passed, the 
amorphous carbonate of lime seems to have become gradually transformed by the 
joint agency of water and carbonic acid into more or less perfectly crystallized 
deposits or concretions, by virtue of which its binding properties must have been 
very considerably augmented. 
The analytical method was described, and the following results were reported as 
expressing the composition of the Roman mortar, and also of the red bricks or 
tiles, which are remarkable for their fine texture and excellent manufacture, 
