1818.] Scientific Intelligence. 461 



difference in the maximum of 23° ; and during the 24 hours a 

 difference of 15° in the means of the extremes. This month 

 terminated with the mean elevation both as to pressure and 

 temperature. 



It is observable that not only the mean pressure, the spaces 

 described, and the number of changes in the direction of the 

 column for the first three months very nearly correspond ; but. 

 also that the quantity of rain and wet days in two of them are 

 also as nearlv equal. 



The temperature from Aug. 1 to 4 gradually increased. On 

 the 5th, the thermometer indicated 83° ; and the following day 

 80° ; after which, to the close of the month, it continued low, 

 with very little variation in the extremes. The range of the 

 barometer until the 26th was also limited ; and on several days 

 it remained nearly stationary, particularly from the 14th to the 

 23d, the amount of its different variations being barely equal to 

 T \,ths of an inch. On the 17th, we had a considerable fall of 

 rain, accompanied with a strong N.E. wind, the quantity from 

 one to five, p.m. and from four to seven, a.m. (the 18th) exceed- 

 ing If inches. At Pickering, eight miles to the N. there was 

 no° ram, while at Scarborough, it fell in torrents nearly three 



hours. 



Though thunder-clouds have frequently appeared, there has 

 been no°storm of electricity observed in this neighbourhood dur- 

 ing the last month. J. b. 



Nets Malton, Sept. 1, 1818. 



XI. Perquadrisulphate of Iron. 



In the Annals of Philosophy, vol. x. p. 100, I have given an 

 account of two salts composed of sulphuric acid and peroxide of 

 iron. The one an orange powder, composed of 2 atoms of 

 peroxide of iron + 1 atom sulphurie acid: the other a red 

 astringent salt, soluble in water, incrystallizable, and composed 

 of 1 atom of peroxide of iron and 3 atoms of sulphuric acid. 

 My attention was lately recalled to this subject by an ingenious 

 suroeon in Glasgow, who brought me some small octahedral 

 crystals of a white colour, which he had obtained by evaporating 

 a solution of protosulphate of iron with an excess of acid repeat- 

 edly in a china cup. He had been able to obtain these crystals 

 only once. All his other experiments to obtain them had failed 

 of success. Hence he was disposed to ascribe the formation ot 

 the crystal to a particular state of the atmosphere with regard to 

 moisture. They had precisely the form of alum crystals. The 

 whole of them scarcely exceeded one gr. in weight ; so that it 

 was impossible to attempt an accurate analysis of them. I dis- 

 solved une of them in distilled water, added a little potash to the 

 solution, and then applied heat. There was a precipitation oi 

 peroxide of iron which I separated by the filter. To the filtered 

 liquid I added a solution of sal-ammoniac. A precipitate oi 



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