84 
Proceedings of the Royal Society 
the percentage of lime, in the precipitate, was 4 per cent, below 
the theoretical quantity required for oxalate of lime. Analysis 
gave 34*1 per cent, of lime instead of 38*3 per cent. ; the salt 
blackening on ignition. There must therefore be an acid along 
with oxalic whose lime salt is insoluble in acetic acid, and, judging 
from the percentage of lime, probably fumaric or mellitic. Further 
experiments on a larger scale must be made before the exact com- 
position of the two acids can be affirmed. 
The application of permanganate potash as an oxidising agent 
in organic chemistry promises interesting results. Many hydro- 
carbons are directly attacked, such as the oil from caoutchouc, 
some of the substances in Young’s paraffin oil, &c., while others, 
having the same composition, resist. It may prove of great value 
in investigating the isomeric hydrocarbons. 
In connection with this subject, I bring before the Society a 
simple mechanical arrangement adapted to illustrate structure in 
the non-saturated hydrocarbons. This little device is the mechani- 
cal representative of Dr C. Brown’s well-known graphic notation. 
A series of narrow thin bars of brass of equal length are taken, and 
every two of the bars clamped in the centre by a nut, so as to 
admit of free motion the one on the other. Such a combination 
represents a single carbon atom with its four places of attachment. 
In order to make the combination look like an atom, a thin round 
disc of blackened brass can be placed under the central nut. At 
the ends of the arms are holes to connect one carbon atom with 
another by means of a nut. The filling up of the places of attach- 
ment may be effected by slipping on the arms round discs of brass 
having a groove attached, and placing the symbol of the chemical 
element on the round projection. A carbon atom would then look 
like the following diagram (see p. 85). 
As it is only intended to express the number of places of attach- 
ment along with the arrangement, when a given number of carbon 
atoms are combined in different ways, it is better to dispense with 
the symbols, remembering that every free arm represents a place 
of attachment. When a number of carbon atoms are joined 
together, all the joints and arms being moveable, it is easy to show 
saturation in a closed or open chain, and the many arrangements 
of the atoms corresponding to the same formula. Although the 
