1871.] 



Heat. 423 



appear to be that these metals were not rendered brittle by low temperatures. 

 Most of the experiments of Joule, Fairbairn, and Spence were made by steady 

 pressure, and therefore cannot be considered reliable when percussive force is 

 brought into play. That there is a difference in these effects, so great that no 

 relation between them can be determined, any one may convince himself by 

 contrasting the tensile strength of glass with its extreme frangibility under 

 percussion. Mr. Brockbank, whose paper drew forth the opinions referred to, 

 took the ground that iron and steel were more liable to break in cold weather, 

 and based his opinion upon percussive experiments. It is obvious, therefore, 

 that his opinion has no weight upon the subject of tensile strength as affected 

 by cold, but it is of great value as confirming experiments previously made to 

 ascertain the effect of cold upon iron and steel subjected to percussion, experi- 

 ments of which Mr. Brockbank was apparently ignorant at the time his paper 

 was prepared. The "Scientific American" has drawn attention to some pre- 

 vious experiments in this direction. In i86g, a "Treatise on Iron and Steel," 

 by Knut Styffe, was published in London, from a translation by Christer P. 

 Sandberg. The translator, however, took issue with the author upon this 

 very question, and denied the applicability of Styffe' s deductions, from tensile 

 experiments, to percussion in cold temperatures, founding his denial upon ex- 

 periments performed by himself in Stockholm under the authorisation of the 

 State Railway Administration of Sweden, in 1867. The results of his experi- 

 ments prove that at io° F. rails will not sustain much more than one-fourth 

 the blow that they will at 84° F. The method of performing the experi- 

 ments, as well as the details of each, are given in tabulated form in a volu- 

 minous appendix to the translation of Mr. Styffe's treatise. Mr. Sandberg con- 

 cluded from his experiments that the brittleness of iron and steel under low 

 temperatures is due to phosphorus present in the metal, and that with purer 

 metal the results would have been different. It is evident that this subject is 

 imperfectly understood, even by the highest authorities, and further extended 

 investigations, with all kinds of iron and steel, must be made before the general 

 effect of cold, as inducing brittleness underpercussion, can be affirmed. Mean- 

 while, it seems to be well settled that the tensile strength of iron and steel 

 when tested by stretching is not lessened by low temperatures. On the con- 

 trary, it would seem from Mr. Spence's experiments to be increased rather 

 than diminished. 



Any light that can be obtained on spontaneous combustion adds not a little 

 to the value of property. Many of the fires charged to incendiarism are really 

 owing to spontaneous combustion, so called. The editors of the " Boston 

 Journal of Chemistry" give some cases illustrating this subject which have 

 come under their own experience. Within the past year, twenty-eight rolls of 

 cotton cloth in a large dyeing establishment were dyed black, and were de- 

 layed a few days before they could be starched and finished. Two of these 

 rolls were discovered to be on fire — not in flames, but in a smouldering condi- 

 tion, or charred into tinder; a third roll was so hot that hands could not 

 handle the cloth, and the wooden roller upon which the cloth was wound was 

 heated almost to the point of ignition. The rolls of cloth destroyed were the 

 first dyed, and consequently had been longer exposed than the others, which 

 in a measure explains why all the rolls were not in the same condition. In 

 the dyeing, the first rolls were dyed without washing, by an oversight of the 

 dyer. This is the point of importance, as the chemical salts were left in the 

 cloth. Logwood, potash, sulphate of copper, and sulphate of iron constituted 

 the dye, and we suggest this explanation as the probable cause of the fire. 

 The potash and sulphate of iron change to sulphate of potash and protoxide of 

 iron, and by the absorption of oxygen from the atmosphere or from moisture 

 in the cloth, this developes sufficient heat to reach the point of ignition. — A 

 fire was discovered in a silk-mercer's shop in London. The fire originated in 

 a lot of black-dyed silk, and was discovered, as in the first instance, before 

 flame had burst out. The conclusion reached was that it was not safe to have 

 black-dyed silk in large masses, and that each piece ought to be so placed as 

 to allow free circulation of air. It is very probable that the explanation of the 

 combustion is the same as in the preceding case. — In trying to get rid of rats in 



