CHEMICAL SCIENCE. 191 



SPONTAKEOUS COJIBUSTION OF PYKOTECHNICAL COilTOIIXDS. 



The following are extracts from a communication of INIr. Thomas 

 Arnall to the "London Pharmaceutical Journal," of Septtmiber, 

 18C6 : "The compositions which are liable to this spontaneous 

 action all contain chlorate of potash and sulphur, with nitrates of 

 Strontia and barj'ta, oxide of copper, etc., as coloring agents. The 

 cause of this action I believe to be, in most cases, acidity, either 

 of the sulphur or some other ingredient used. It is well known 

 that most of the flour of sulphur, as met with in commerce, has a 

 slightly acid taste. This acidity has been attributed to atmospheric 

 oxidation from long exposure, but more probably is caused by 

 partial combustion during sublimation. Now, supposing sulphur 

 containing a slit^ht trace of sulphuric acid to be mixed with chlo- 

 rate of potash, it will liberate a corresponding quantity of chloric 

 acid ; this at once oxidizes more sulphur, and so the mutual reac- 

 tion goes on until the mixture ignites. But we have also nitric 

 acid in combination, and the nearly anhydrous vapors of these two 

 acids will sufiiciently account for "the heating and ignition of the 

 compounds in which they are evolved. 



"I have been informed by jn-actical pyi-otechnists that they 

 never use sublimed sulphur, but buy it in roll, and powder it for 

 use when wanted ; and I believe that latterly the sulphur has been 

 superseded for indoor uses by a mixture of shellac and resin. This 

 has the merit of comj^arative safety, although the brilliancy of the 

 colors will not bear comparison with those formuliB where sulphur 

 is used. 



•' These remarks do not apply to a most dangerous compound 

 for purjile fire, which contains ehloi-ate of potash, sulphur, nitrate 

 of strontia, and anhydrous sulphate of copper. Although tlie color 

 is exceedingly beautiful, I can enumerate five deaths i'rom explo- 

 sions, in addition to other cases not fatal, where this formula was 

 in use ; and I have had it ignite four times in my own experi- 

 ments. In this case no acidity of the ingredients seems requisite. 



" I am disposed to attribute the ignition, first, to the anhydrous 

 sulphate of copper attracting moisture i'rom the air ; next, t(j double 

 decomposition of the copper salt and chlorate, ultimately forming 

 chloride of copper (possibly bichloride), with evolutionof chloric 

 oxides or chloric acid. I have substituted black oxide of copper 

 for the sulphate, and the mixture has not shown any tendency to 



Ignition. 



I believe that disaster may be frequently averted by first mix- 

 ing a few drachms of the ingredients in a mortar. If the ingre- 

 dients are pure, no smell should be perceived ; but if acid be 

 contained either in the sulphur or other ingredients, a peculiar, 

 somewhat ozonic odor will arise, which may be considered as 

 indicative of danger." 



SPONTAiSTEOUS COMBUSTION OF COAL ON BOARD SHIPS. 



The committee of Lloyd's Salvage Association has issued the 

 subjoined report upon this subject, which has caused the destruc- 

 tion of so many vessels : — 



