CHEMICAL SCIEXCE. 247 



are produced over the entire surface of the earth, especially over un- 

 cultivated tracts, and are the means provided by nature to dissolve 

 the mineral food of plants ; they are also amongst the chief causes of 

 the exhaustion of soils. The author then alluded to Prof. Way's ex- 

 amination of some of the green-sand strata of Surrey, known as fire- 

 stone, a light and porous rock, containing silica in a soluble state. 

 It was well known that common sandstone, quartz, or rock crystal 

 were not acted upon by potash or soda at ordinary temperatures ; but 

 of the firestone 30 per cent., and sometimes 50 or 70 per cent, may 

 be dissolved. In all such cases the silica must have been originally in 

 a state of chemical combination with lime, alumina, or something else, 

 which has been subsequently removed. The silica in the rotten-stone 

 was soluble, but he had never met with instances of black marble in a 

 bedded state converted into rotten-stone. He believed, however, 

 that a similar cause, operating over a wide area, and during a lon<* 

 period, had produced the altered condition of the firestone. Prof. 

 Johnston then alluded to the nodules of phosphate of lime in the green- 

 sand and crag, and suggested that the phosphorus had been derived 

 from animal remains in higher strata, dissolved out by acids, and rede- 

 posited at a lower level. The last example was the fire-clay of the 

 coal measures, a stratum almost universally found beneath beds of 

 coal. It differs from the other clays both in color and composition, 

 being whiter, and containing less of those substances which acid bod- 

 ies could dissolve, viz., the earthy bases, which would render the clay 

 fusible in fire ; the condition of the fire-clay might be accounted for by 

 the action of acids developed during the production of the vegetable 



matter now forming coal. 



MANUFACTURE OF STARCH. 



Some improvements in the manufacture of starch have recently 

 been patented by Mr. Tucker, of Belfast, Ireland, which relate essen- 

 tially to the application of certain salts, both alone, and in combination 

 with some mineral acids, for the more effective separation of the pure 

 starch from the glutinous and other foreign matters, with which the 

 starch itself is originally combined ; as well as to the neutralizing the 

 injurious effects of the vegetable acids generated in the process of 

 starch making, and the increase of the produce of good starch from a 

 given quantity of wheat. By the same means, Mr. Tucker is also 

 enabled to render any pure water suitable for starch making, although 

 in its natural state such water may be ill adapted for this purpose. 



After the wheaten meal, or reduced grain, has been submitted to 

 the usual process of fermentation, and has been washed, to separate 

 the bran from the rest of the elements of the treated substance, the 

 starchy liquor is run into a receiver or vat, where it is allowed to 

 remain for about the space of thirty-six hours for precipitation. The 

 supernatant liquor is then run off or removed, and the precipitate is 

 broken up. Then a solution of sulphate of soda, or Glauber's salts, 

 in boiling water, is prepared, in the proportion of about twelve pounds 

 22* 



