152 History of Mechanical Inventions and 



time ; yet it must be allowed, that its power of inflammation is not equal 

 to the tinder, although it most readily takes fire, and, of course, is quite 

 equal to the purpose of igniting a match. 



With regard to the tinder, I may mention that I once prepared a small 

 portion (by chance) that inflamed the gas as easily and quickly as the 

 spongy platinum ; but having no time, at that period, to prosecute any 

 farther experiments on the subject, I must be content with merely men- 

 tioning the fact as it occurred. At the same time I may add, from recol- 

 lection, that this piece of rag was used in wiping the vessel in which the 

 ammoniacal precipitate had been prepared, and consequently may have 

 imbibed a portion of the precipitate that was unavoidably left in the bason. 

 I think the instrument, with this very cheap method of preparing the 

 substance, or tinder, will prove a most useful appendage to a bedroom, 

 seeing that it has elegance, cheapness, and compactness to recommend it. 



When the impregnated tinder is employed, it may be proper to remark, 

 that a larger jet is required at first to ignite it, and then a continuance of 

 a very small stream is needful for the inflammation of the gas. The same 

 precaution is necessary with one that I forgot to mention, that is paper. If 

 the filtering paper, on which the precipitate is washed and dried, be burnt 

 to redness, and then covered so as to exclude the access of common air to 

 it, then it forms, when cold, as good an article for the inflammation of the 

 gas as that prepared from rags. But if the charcoal preparation be had 

 recourse to, a considerable waste of gas must be expected before inflamma- 

 tion takes place ; yet if that is not required, ignition may be produced 

 with a small portion indeed. All these preparations have a great advantage 

 over the spongy platinum, for when they are once ignited, they continue 

 for a very long time to be so, whereby time is afforded to apply a match, 

 if a light is all that is required ; whereas the spongy mass goes out instant- 

 ly when the gas is stopt ; and, on several occasions, when the gas was 

 nearly expended, or, in other words, the pressure was so small as not be 

 sufficient to produce flame by the platinum, on substituting the tinder it 

 was ignited instantly, and by it a match kindled, which may answer the 

 purpose for the time. 



6. On the Use of Granite fur Railways- In a Letter from John Gibb, 

 Esq. Civil Engineer, to John Robison, Esq. F. R. S. E. 



SlK, 



I trust you will excuse me for addressing you on the subject of railways. 

 But the unprecedented demand, and consequent high price of cast-iron, 

 occasioned, perhaps, partly by the vast quantity required for the distribu- 

 tion of gas, together with the increasing prosperity of the country ; having 

 created an extraordinary demand for new manufacturing establishments, 

 will, I fear, greatly retard the progress, and increase the expence of the 

 numerous railroads now contemplated in various districts of Great Britain, 

 I have, therefore, been induced to turn my attention to this subject, and I 

 beg to submit the annexed sketch, Plate I. Fig. 8, for your consideration, 

 which, according to my estimate, will have the advantage over the present 



