236 Dr. Mallet on the production of Sulphuretted Hydrogen. 



I have for some time devoted a good deal of attention, namely, 

 the action of" air and water on iron," and other metals. 



To Mr, Daniell must be awarded the merit of having first 

 pointed out the very extended limits in which sulphuretted 

 hydrogen thus occurs, and of indicating its highly probable 

 connexion with pestilential diseases ; but the claim which is 

 apparently made in this paper (see page \\ et passim) by its 

 author, to be the first who has pointed out the undoubtedly 

 true source of this gas in the decomposition of sulphates by 

 decomposing organic matter, cannot, I think, be sustained. 



In the second report on the action of air and water, 

 (whether fresh or salt) on iron, read at the last meeting of the 

 British Association, and since published, section 171 — 172, 

 the production of sulphuretted hydrogen in this way will be 

 found fully pointed out, and its theory in the case of the iron 

 salts even much more extended than had before been done ; 

 while the mere fact that the sulphates are deoxidized by or- 

 ganic matter in certain states has been observed years since, 

 and even the formation of pyrites by the action of animal 

 matter in putrefaction on the sulphates of iron ; a case of 

 which is, I think, recorded in Thompson's Annals of Philo- 

 sophy. I have remarked that even insoluble sulphates, such 

 as gypsum, can be decomposed in this way ; but the power 

 of decomposing either soluble or insoluble sulphates depends 

 upon the peculiar state of decomposition in which the vege- 

 table organic matter is found, and does not seem to me to 

 take place, unless when carbonic acid is also present on the 

 water, which it generally then is as a product. 



About nine years ago the Directors of the Dublin and 

 London Steam Marine Company requested me to examine 

 the copper sheathing of their steam ship " Thames," since 

 lost off " The Lizard," which had in a very short time cor- 

 roded into holes, and on the ground of which they were about 

 taking proceedings against the parties who supplied the cop- 

 per. I found that the inside of much of the copper was lined 

 with black sulphurates, such as Mr. Daniell describes; and 

 on examining the " berth" where the vessel lay when in this 

 port, I found it was over a bank of soft silt, and opposite a 

 large sewer which constantly discharged putrid matter : to 

 this I then attributed the decay of the copper, and advised the 

 removal of the vessel to another berth, which was done after 

 recoppering, and with the result desired: this, therefore, 

 confirms the views on this subject Mr. Daniell has so well 

 stated ; but I feel myself compelled to differ with this gentle- 

 man as to the power of zinc permanently to protect copper 

 from corrosion in sea-water thus charged with sulphuretted 



