SPONTANEOUS COMBUSTION OF PYROTECHNICAL COMPOUNDS. 163 
of lubricating oil to crude oil being known, tbe amount of paraffin in tbe 
crude oil is readily calculated. The paraffin (“ paraffin scale ”) thus obtained 
is not quite pure, retaining some colouring and odorous matters. By subse¬ 
quent treatment with sulphuric acid and soda, or recrystallization from petro¬ 
leum-spirit, it may be obtained colourless and inodorous, but this operation 
is generally unnecessary of performance by the analyst, as but little by weight 
is lost in the purification. Its melting-point should, however, always be de¬ 
termined, as the higher this is the more valuable the paraffin. For this ] 3 ur- 
pose a small quantity of the melted paraffin is drawn up into a capillary tube 
ten or twenty centimetres long and about half a millimetre in diameter, the 
tube immersed in cold water and the vessel containing the water heated until 
the minute cylinder of paraffin changes from the condition of an opaque solid 
to a transparent liquid. By means of a delicate thermometer placed in the 
water the point of change can be determined to the tenth of a Centigrade 
degree : it varies from 40° to 60° C. 
In conclusion I would recommend that in reporting on the oil-value of a 
coal, etc., the chief products be described respectively only by the terms 
“ spirit,” “ photogen,” “ lubricating oil,” “ paraffin,” and “ coke,” and that 
the specific gravity, at 15°'5 C., and boiling-point of each of the liquids, and 
the melting-point of the paraffin be always given. The term “spirit” is al¬ 
ready common for this the liquid of lowest boiling-point, and is sufficiently 
indicative of its use as a substitute for sxDirit of turpentine. “ Photogen ” 
is definite as a distinctive name for the burning-oil or ‘ light-producer,’ and 
already more restricted in its application than its synonyms “ paraffin-oil,” 
“ lamp-oil,” “ illuminating-oil,” “ heavy naphtha,” “ solar-x)etroleum,” “ solar- 
oil,” etc. etc. In the International Exhibition of 1862 (see Juries BejDort, 
class II. section A.) solar-oil was in one place described as the coal-product 
having a specific gravity of 0’833 or 0‘835, in another as the product con¬ 
taining no oils of less specific gravity than 0‘870 or more than 0‘920. Such 
discre^Dancies are most confusing, and should be avoided. If the results of 
the examination of coal, lignite, shale, etc., and petroleum be reported in the 
manner above indicated, the amount of acid and alkali used and the loss in 
distillation and in x^urification being also given, there will not be much diffi¬ 
culty in determining the money value of the raw material, as the cost of 
precting and maintaining oil-works can now be readily ascertained, and the 
erices of ail materials and products are almost daily published. 
17, Bloomsbury Square, London. 
ON THE SPONTANEOUS COMBUSTION OF PYBOTECHNICAL 
COMPOUNDS. 
BY” THOS. ARNALL, M.P.S., WEDNESBURY. 
In the year 1843, I forwarded a note upon this subject to the editor of the 
‘Pharmaceutical Journal,’ which was printed in vol. iii. page 38. 
At that time I had not leisure to continue the experiments I purposed to 
make, and the subject appears to have rested since 5 at all events, little infor¬ 
mation has been published, so far as I am aware. 
Since the above date I have had to make these “ coloured fires ” by the hun¬ 
dredweight, and having had several accidents I think I have detected some of 
the causes, and can also explain the comparative immunity of firework establish¬ 
ments from accidents arising from this cause- 
The compositions which are liable to this spontaneous action all contain 
chlorate of potash and sulphur, with nitrates of strontia and baryta, oxide of 
M 2 
