MINERALOGY. 45 



a black or blackifh brown powder, and becomes 

 alfo of the lame colour in the fire. However, 

 when this iron ore contains only a very final! 

 quantity of iron, it may be rfed to make lime * 

 though it becomes of a grey colour, juft as when 

 clay is mixed with limeftone, as is the Alfwarftett, 

 in which there is always fome mixture. 



It feems as if the white iron ore might be ufed 

 with advantage, and preferably to others, is 

 making cement, whofe conftituent parts are al- 

 ways lime and iron 5 but neither is it apt to con- 

 crete, when once mouldered •, nor by experiment* 

 made for that purpofe, has it difcovered any qua- 

 lity of binding or uniting : we muft, therefore* 

 examine other fubftances, which may better an? 

 fwer the intention •, and then it will be found, that 

 iron, which is too much in its metallic ftate, h 

 eafily affected by the vitriolic acid, whereby the 

 cement made of it would in length of time be 

 diflblved, and rendered ufelefs •, nor, on the con- 

 trary, is a perfectly calcined iron of fo much for* 

 vice, as when it has fome of its phlogifton left. 

 For inftance, a cement prepared from the flags of 

 a fmith's forge, mixed with lime and coarfe land* 

 has been found, in fome refpect, to anfwer all the 

 good effects expected, it depending only on time 

 to (hew, if it is durable enough. , The 'Terra 

 Puzzolana and Terras are nothing elfe than iron 

 ores mixed with a yet unknown earth. Its effect, 

 however, in the cement, may, perhaps, depend 

 only on the iron, which has been reduced into a 

 particular fubftance by means of fubterraneous 

 fires, for their native places retain evident- %n$ 

 thereof. 



If the (late in Henneberg, or Kinnekulle 

 in the province of Weftergotdand, mould 



happen 



