240 CHARCOAL OF MAIZE. 



^iins. The residuum was still very black, pasty, and ad- 



^ hered to the iron with which it was stirred. On washing it 



was reduced to two drachms 8 of rains. 



toatoutone. These two drachms 3 grains were calcined another hour, 



which reduced the weight to about 6o grains ; and were theu 



Gave ISgrs.of lij^.jviat^^]^ The lixiviums mixed t^opetheryielded ISi^rainsofa 

 saline extract. ,. , • ^ i • i .,.,... 



salnie extract, the taste or which was not perceptjnly alkalme. 



Phosphate of These IS grains, redissolved and drie^l, would not crystul- 

 potasi. ij^^^ and were reduced to 14. Suspecting that tlie potash 



was saturated with phosphonc acid, I dissolved it in distilled 

 vinegar, and afterward treated it with alcohol. This opera?* 

 lion reduced it to 11 grains of that acidulous phosphate, 

 whici. crystallizes in letraedral pnsms termin;ited by similar 

 pyramids. I foget whether the faces of the pyramids anr 

 EwCiCd to the faces or edges of the prisn>* 



If 10 drachms of chavcou!, the produce of 41 of maize, 



gave 14 grains of phosphate, 100 drachms of maize v.ould 



J'icld but 34 or 35 gtaiiis, which is far from 40 per cent, as 



itienticned in Dpiamctherie's Journal. So great a ditference 



could not have escaped such a man as de Saussure: it^ must 



have been nn errournf the press therefore, or of the manuscript. 



The obstinacy with which the cliarcoal of maize resistsbiirn- 



in^ is astonisinnj;: animai charcoal could not exhibit more. 



Charcoal frprh i he same plaint affords a ciiarcoal of very different kind. 



th^ sMlk bums The charcoal of the stalk, triturated with five sixths its 



the time. weight of saltpetre, is consumed in a tube of a given diameter 



in '28 seconds, /Vs milar mixture made with the charcoal of 



the grains rev^u-ret, 52 seconds for its being consumed in the 



same tube* 



To Correspondents* 



The comiriiracat'on with winch N. R. D. promises to fa-- 

 vour me will be Very acceptable. I have likewise to thank 

 him for his concluding hint, and shall certainly avail myself 

 of the sour( e it points out. 



Mr. Cayley*s communication is received, but on account 

 of the engraving it could not be inserted in the present 

 month. 



I hope to be able to give some correct Observations and 

 Resalts in oar next respecting the Comet, which is at pre- 

 Wiut visible. 



