Chemical Science. 463 



by Dr. Hibbert. Without wishing to undervalue Dr. Hibbert's 

 labours, we must, injustice to Dr. Trail, remark that he pointed 

 out the existence of this mineral in Unst many years ago. It 

 is true that he calls it magnetic iron ore, but the existence 

 of a chromate was then unknown." 



In reply to this statement I have first to observe, that both 

 magnetic iron ore and chromate of iron are found abundantly 

 in the island of Unst. But waving this circumstance, I am 

 totally unacquainted with any report published by Dr. Trail 

 upon the mineralogy of this island, in which the existence even 

 of magnetic iron ore was pointed out. Dr. Trail's description 

 of the rocks of Shetland appeared in Mr. Neil's tour through 

 that country in the year 1803, and from this work it was copied 

 verbatim into the 15th volume of Nicholsoji's Journal. It will 

 be there found that not a word is mentioned of any metallic 

 substance occurring in the island of Unst except bog iron ore, 

 with which mineral it is needless to observe that the chromate 

 of iron could not possibly have been confounded. 



I can consider the information which gave rise to your notice, 

 in no other light than as an unintentional mistake. On this 

 account, any further remarks that suggest themselves in obvious 

 refutation of the statement are, at present, better suppressed, 

 since they might only have the improper tendency of leading 

 you to imagine that I entertain a contrary supposition. 



I am, &c., 

 10, Argyle-square^ Edinburgh^ Samuel Hibbert. 



Nov. 22, 1820. 



22. On rendering Cloth incombustible. — M. Gay Lussac has 

 proposed a means of rendering the various tissues of cloths, 

 stuffs, ^c, incombustible ; and the means he recommends ap- 

 pear superior to those which as yet have been proposed ; that 

 the combustibility of these substances is diminished by their 

 having been immersed in solution of certain salts, as of alum, 

 muriate of soda, Sfc, has been long known. M. Gay Lussac 

 considered that those salts should possess this property most 

 eminently, which entered most readily into fusion, being enabled 



