incident to Steam Boilers. 133 



That sudden inflammations of gas in the chimneys of these 

 engines does take place is, I believe, sufficiently obvious. By night 

 it is observable that bursts of flame suddenly illuminating the 

 surrounding scene, and rising to a considerable height above 

 the summit of the stack, are seen to emerge, and after a blaze 

 of some minutes diminish and retire into the flue, leaving all 

 once more in pei'fect darkness. This effect I certainly do not 

 recollect to have noticed where the coal is less bituminous. 

 The fact is not, perhaps, of much importance ; but it has been 

 remarked upon by some who have witnessed the accident I 

 have described, and has been discussed by them in reference 

 to it, and therefore it is right to mention it. 



Though I have been led to describe the bursting of boilers 

 where what is called high-pressure steam has been used, I by 

 no means think that boilers are safer because the steam in 

 them is supposed to be limited to a lower degree of expansive 

 force. High-pressure boilers are or ought to be very strong, 

 and can only give way by a great increase offeree beyond what 

 they are calculated to resist, which should happen but seldom. 

 Low-pressure boilers are from their construction very weak, 

 and a little carelessness raises the power of the steam within 

 them to the bursting point, and when they give way the con- 

 sequences are often very fatal. Not to mention other instances, 

 I may remark, that about twelve months since one of the old 

 spherical construction, which is still much used in some parts 

 of the kingdom, burst at a mine in Flintshire about 7 miles 

 from the Mold Mines, and occasioned the death of 16 {)er- 

 sons : it was replaced by two smaller boilers of the second 

 kind I have described, and high-pressure steam applied with 

 good effect to the engine, and with perfect security. 



XXX. On the Crystalline Forms of IVagnerite. By A. Lew, 

 Esq. M.A. F.G.S.* 



/^NE of the rarest species in mineralogy is that which has 

 ^-^ been named Wagnerite, the chemical composition of 

 which according to the analysis of Fuchs it as follows : 



Phosphoric acid 41*73 



Fluoric acid 6*50 



Magnesia 46-66 



Oxide of iron 5* 



Oxide of manganese 0*50 



100-39 

 A large and well-defined crystal of this substance is pre- 

 served in Mr. I leuland's private collection, and it is the only 

 * Communicated by the Author. 



one 



