Mr James Macadam's Analysis of Pottery. Til 



lish, and afterwards reprecipitated from its state of solution 

 by adding chloride of ammonium. 



The lime present was precipitated as oxalate; this was 

 converted into the carbonate by ignition, and estimated as 

 such. 



The magnesia was precipitated as the ammoniacal phos. 

 phate — 



(2 Mg O NH 4 P0\) 



This, after ignition, was collected as the bibasic phosphate 

 (2 Mg PO''). 



The water and organic matter were estimated according 

 to the usual methods. 



102-15 



The increase here represented may, to a great extent, be 

 accounted for by the fact, that nearly all the iron exists in 

 the pottery as protoxide ; whereas, during the analysis, it was 

 converted into the sesquioxide, and weighed as such.* If the 

 quantity of iron present had been calculated as protoxide 

 {which vwuld be much nearer the truth), its amount would 

 have been 1*46 less than that stated above, which would re- 

 duce the amount of gain during the analysis to -69. 



It is probable that this pottery was not made from the use 

 of any one material found native, but that it was manufac- 

 tured from a mixture of pulverised silica, ferruginous clay, 

 «,nd organic matter ; the silicic acid of which, afterwards com- 



* It appeared more desirable to collect all the iron present as the sesqui- 

 oxide, than trust to the accuracy of any of the processes extant, for determin- 

 ing the respective quantity of each oxide when both are present. 



VOL. XLII. NO. LXXXIV.— APRIL 1847. T 



