Mr. Telford o?i the Ejects of removing Lotidon Bridge. 21 



bable that they have not been formed by crystaUization in 

 cooling from a state of fusion, but have received their succes- 

 sive increments by reduction of the oxide dissolved in the slag 

 around them : a mode of formation to which we must have 

 recourse for conceiving rightly the formation in nature of many 

 other metallic crystals. 



Since the date of this communication, the liberality of Mr. 

 Anthony Hill, of Merthyr Tydvil, has supplied me with a 

 larger quantity of the slag which formed the subject of my 

 first experiments, and has enabled me to determine the spe- 

 cific gravity of metallic titanium to be 5-3. For this purpose, 

 the vitreous part was fused with a mixture of borax and sub- 

 carbonate of soda in about equal quantities, and was then dis- 

 solved in muriatic acid, which also removed a quantity of me- 

 tallic iron, and left the titanium freed from extraneous matter. 

 Though great part of what was thus obtained from the in- 

 terior of the slag was in a pulverulent state, the quantity, 

 which amounted to 32 grains, and displaced 6-04 of water, 

 was sufficient to preclude any considerable error. 



I have moreover learned that metallic cubes, similar to those 

 which I have above described and examined, were more than 

 20 years since observed in a slag at the Clyde iron-works in 

 Scotland ; that a small quantity has also been met with at the 

 Low Moor iron-works, near Bradford in Yorkshire ; and at 

 the Pidding iron-works, near Alfreton in Derbyshire; and 

 that some good specimens have been obtained from Ponty- 

 pool in Monmouthshire ; but it does not appear that any one 

 has ascertained or even suspected the real nuture of this sin- 

 gular product. 



VIII. Repo7t o/Thomas Telford, Esq. on the Effects ivhich 

 mil be produced on the River Thames hy the Rcbnilding of 

 London Bridge. 



IN consequence of the authority given me by the resolution 

 of the Committee for letting the Bridge- House Estates, 

 dated the 7th of March last, I immediately took measures to 

 get an accurate survey made of the river, its banks and ap- 

 pendages. For diis })urpose I employed two persons expe- 

 rienced in making similar surveys, viz. one for the district from 

 London Bridge to Putney, and the other from Putney to 

 Teddington Lock ; and in order to ensure accuracy and jiro- 

 per connexion and uniformity, I caused one of my own assist- 

 ants, also accustomed to rivei' surveys, to carry levels from 

 London Bridge to Teddington Lock, and 1 have myself su- 

 perintended 



