288 EIGHTH REPORT — 1838. 



years afterwards : every part of the iron still covered with the 

 tar was found sound and untouched as when put down ; but the 

 ground faces, which had not been tarred, were softened and con- 

 verted into plumbago to the depth of | of an inch. 



This interesting and important observation shows that, where 

 abrasion does not interfere, if Ave could get any coating to ad- 

 here to the iron which would be impervious to air and water, • 

 the preservation of the metal would be effected in the best and 

 simplest manner. Unfortunately, many difficulties oppose this, 

 and few, if any, varnishes can be obtained which will spread 

 over the iron withovit leaving uncovered spaces or microscopic 

 pores . 



Professor Lampadius long ago directed his attention to this 

 point, and, in the Annales des Arts et Manufactures, published 

 the composition of a paint or varnish for the preservation of 

 iron from rust, the basis of which is sulphate of lead and sul- 

 phate of zinc ground M'ith plumbago and oil. It is difficult, 

 however, to see the precise point aimed at by this composition. 



82. The paints and varnishes which have been placed in pro- 

 cess of experiment in the above five various conditions are seve- 

 ral of those most ordinarily in use, with the view, that as no- 

 thing certain is known upon this branch of the subject, the fate 

 of these coverings, many of whose other properties are well 

 known, may afford leading indications as to the direction in 

 which improvement may be sought. 



83. As yet it has been impossible to arrange any experiments 

 upon a large scale upon wrought iron, nor indeed to collect suf- 

 ficient specimens ; but there has been included in each of those 

 five boxes a single parallelopiped, all of equal size, and cut from 

 the same bar ; it is of what is called common Welsh bar iron, 

 or No. 1, and was made at Dowlais Iron-works, South Wales. 



This bar I have called " The Standard," and the remainder 

 of it, which is some feet in length, is proposed being deposited 

 with some learned body to be appointed by the British Asso- 

 ciation. 



Now this standard being placed in each box in circumstances 

 precisely similar to the rest of the specimens, it is intended to 

 take the action of the sea and fresh water upon it as unity, and 

 refer their action upon all the other specimens to this, by which 

 means not only will this whole series of present and projected 

 experiments on wrought and cast irons be numerically compa- 

 rable most conveniently by the engineer, but any future experi- 

 menters upon novel makes of iron, or upon foreign ones, can, 

 by reference to the standard bar in possession of the Associa- 

 tion, make their experiments comparable with these. 



