122 SEVENTH REPORT—1837. 
The following are the specific gravities of eight specimens of 
cold blast iron :— 
Ist. Muirkirk. ..). . « «6 (6 6°410 
Phd. Dittoa os) 66) MSS 
Srd. Ditto.) a aS 
Ath itera oh a ee ee 
SU a CGE ai. el a fe 2 OOS 
6th. From pyrites . . . . . . 6°9444 
Vths: BromGarron> o)a5 2. i SPRSS 
8th. Clyde Iron Works . . 7°0028 
The specific gravity of the Muirkirk iron is s considerably less 
than of that smelted at Carron and the Clyde Iron Works ; the 
mean of the 8 specimens is 6:7034. 
It has been hitherto supposed that the difference hetween cast 
iron and malleable iron consists in the presence of carbon in the 
former, and its absence from the latter ; in other words, that cast 
iron is a carburet of iron. But inallthe specimens of cast iron 
which we analyzed we constantly found several other ingredients 
besides iron and carbon. Manganese is pretty generally pre- 
sent in minute quantity, though in one specimen it amounted 
to no less a quantity than 7 per cent. ; its average amount is 2 
per cent. Si/icon is never wanting, though its amount is exceed- 
ingly variable, the average quantity is about 1} per cent. ; some 
specimens contained 3+ per cent. of it, while others contain less 
than a half per cent. Aluminum is very rarely altogether absent, 
though its amount is more variable than that of silicon. Its ave- 
rage amount is 2 per cent. ; sometimes it exceeds 43 per cent.,and 
sometimes it is not quite =,,5th part of the weight of the iron. 
Calcium and magnesium are sometimes gel but very 
rarely, and the quantity does not much exceed }th per cent. 
In a specimen of cast iron which I got from Mr. Neilson, 
and which he had smelted from pyrites, there was a trace of 
copper, showing that the pyrites employed was not quite free 
from copper; and in a specimen from the Clyde Iron Works 
there was a trace of sulphur. The following table exhibits the 
composition of six different specimens of cast iron, No. 1, ana- 
lyzed in my laboratory, either by myself or by Mr. John Tennent. 
Muirkirk. | Muirkirk.|Muirkirk,| Pyrites. | Carron. Clyde. Mean, 
Tron siscasses 90°98 | 90°29 | 91°38 89-442 | 94:010 | 90°824 | 917154 
Copper ...... ——_— | —_ | — 0-288 | —— —— 
Manganese...| _—— 714 2°00 —— 0-626 2°458 2:037 
Sulphur ...... — |= —__ | — _— —_— 0°045 
Carbon ...... 7°40 1:706 | 4°88 3°600 3°086 2°458 3°855 
DIHCR sescccces 0°46 0°830 | 1:10 3°220 1-006 0:450 1177 
Aluminum . 0:48 0016 | —— 3°776 1032 4602 1651 
Calcium ...... —— 0:018 | 0°20 _— —_— — 
— — 0°340 
Magnesium —_— | —_— | — 
