Royal Society. 327 



existed respecting the views stated by the author in his former 

 papers, and with a reply to the strictures of M. Arago on those views. 

 The result of the geometrical measurement of one particular au- 

 rora, gave as the height of its upper edge, 5693 feet above the level 

 of the Manse at Alford ; and the vertex of its arch was found to be 

 14,831 feet northward of the same place. The vertical extension of 

 the fringe of streamers was 3212 feet; leaving 2481 feet for the 

 height of the lower edge above the level of Alford. The tops of the 

 Corean hills, immediately under the aurora, are about 1000 feet- 

 higher than that level ; so that the lower edge of the arch was only 

 1500 feet above the summit of that range of hills. 



4. " On the Phosphates." By John Dalton, D.C.L., F.R.S., &c. 

 The author takes a review of the labours of preceding chemists 



which bear upon the subject of the atomic constitution of phospho- 

 ric acid, and the salts in which it enters as a constituent ; and shows 

 their conformity with the views he has already advanced on the sub- 

 ject. A supplement is added, giving an account of the elFects of 

 various degrees of heat on the salt denominated the pyrophosphate of 

 soda. 



5. " On the Arseniates." By the Same. 



The author here examines the conformity of the results of the 

 analysis of the salts of arsenic with his theory, in the same manner 

 as he has done with the phosphates in the preceding paper. 



6. " On the Constitution of the Resins." Parts II. and III. By 

 J. F. W. Johnston, Esq., F.R.S.* 



In this paper the author, pursuing the train of investigation of 

 which he has already given an account in a former communication, 

 gives tabulated results of his chemical examination of several va- 

 rieties of gamboge, and formulae expressing their chemical constitu- 

 tion. A detailed account is given of the properties of the gambodic 

 acid, and of the salts it forms with various bases, such as the gam- 

 bodiates of potash and soda, of ammonia, and of different earths and 

 metals, particularly lime, strontia, magnesia, lead, copper, zinc, and 

 silver. He concludes from this investigation that the most probable 

 formula for gamboge is C^q Ho^ Og. In the analysis, however, of 

 every specimen, there occurred a deficiency of carbon, amounting to 

 nearly one per cent. ; a deficiency supposed to be due to a change 

 produced during the preparation of the natural resin for the market. 

 By a heat of 400° Fahr. gamboge undergoes a partial decomposi- 

 tion ; a resin, soluble in alcohol, and another resin, insoluble in 

 that menstruum being formed : the formula representing the latter 

 being C^g H22 Oy. Gamboge forms with the metallic oxides nume- 

 rous salts, the existence and constitution of which, however, the ex- 

 periments of the author only render probable. 



The inquiries of the author were next directed to the chemical 



constitution of the resin of guaiacum, and to the properties of the 



salts it forms with various bases. He then examines the acaroid 



resin, which exudes from the Xanthorrhvea hastilis, and is often 



* See our last volume, p. 340. 



