480 f'HILOSOPHICAI. TKANSACJTIONS. [aNNO 1779- 



acquired the liardness of" common grit stotie, and retained the colour of the 

 sand, with very little tincture of the iron ochre : and by the part which was left 

 free from the incrustation it appeared most probable, that the horse-shoe had not 

 been buried there many years, but had very recently acquired this incrustation 

 on that part only that was most exposed to the washing of the sea water. 



Now, all these facts put together scarce leave any doubt but that iron, and 

 solutions of iron, greatly promote and hasten the progress of all kinds of petre- 

 faction ; and therefore we may fairly infer, that whereas iron is of such manifest 

 use in the progress of vegetation, that plants are indebted for their green colour, 

 and for many of their valuable qualities, to its being intimately mixed in their 

 substance; and as it is obviously useful also in the animal system, and may be 

 extracted by the magnet from the ashes of animal substances ; so it is no less 

 useful in the consolidation of stones and marble in the fossil world. Mr. Pryce, 

 in a very useful and curious treatise of mineralogy, has also lately shown it to be 

 equally useful in the mineral world, by forming a proper nidus for the assem- 

 blage of the most valuable metals, and thus attracting and uniting them. This 

 metal, therefore, seems to be almost universally one of the greatest bands that 

 unites the several parts of matter, and one of the most useful and important 

 of substances in the world. 



If iron and the solutions of iron do thus contribute to tiie induration of 

 bodies, such solutions must probably have that tendency in every stage of those 

 bodies' existence ; and therefore it seems likely that the fine ornamental carvings 

 in Portland, or other stone, might be much hardened, and preserved for a much 

 longer time than has been usual, from the injuries of the weather, by being 

 washed and brushed over by water, in which is infused a solution of iron. And 

 perhaps even the softer kinds of stones might have been preserved by this means; 

 and the venerable remains of that fine pile of building, Henry the 7th's chapel, 

 might have been saved from the destruction with which we now see it ready to 

 be overwhelmed. It is very probable also, that common sea sand, with a very 

 small admixture of a solution of iron, may at length, without any great ex- 

 pence, be converted into a useful species of stone, and be applied to the purpose 

 of covering the fronts of houses even more durably, and in as beautiful a manner 

 as some of the late invented stuccos ; and even those stuccos may be improved 

 by means of the same mixture. 



F. Account of Dr. Knight's Method of making Artificial Loadstones. By Mr. 



Benjamin Wilson, F. R.S. p. 5 1 . 



The method was this : having provided himself with a large quantity of cleag 



filings of iron, Dr. K. put them into a large tub that was more than J filled with 



clean water : lie then, with great laboui-, worked the tub to and fro for many 



