230 Intelligence and Miscellaneous Articles. 



The remarkable fact of a recurrence of cusps observed by Mr. 

 Airy in 1842, and his explanation of it, should be attentively 

 coneidered. See Ast. Soc. Notices, v. 296. 



8. If possible, accurate measures should be taken of the apparent 

 diameter of the dark disc of the moon upon the sun, which may be 

 expected to be greatly less than the truth, owing to the irradiation 

 of the sun's light. 



9. It should be noticed whether any external luminous arch is 

 formed over the part between the cusps, a little before the first junc- 

 tion and after the final separation, and the colour of the light. 



It was observed, and appeared brown to De Lisle (Phil. Trans., 

 1748, 490), reddish in other cases (Ast. Soc. Mem., i. 144, 

 X. 37), Siadi purple in others (ib. x. 16). 



ON THE PREPARATION AND COMPOSITION OF THE SALTS OF 

 ANTIMONY. BY M. E. PELIGOT. 



Sulphates of Antimony. — When oxychloride of antimony (CI Sb^O-) 

 is treated with hot concentrated sulphuric acid, a salt is formed 

 which is deposited in acicular crystals, hydrochloric acid being at 

 the same time evolved. This salt, as well as another sulphate to 

 be described, can only be obtained in a dry state by long remaining 

 in vacuo, or in perfectly dry air upon porous plates of pipe clay. 

 These plates were heated to redness before the crystalline magma 

 was placed upon them, and they were left to cool in air deprived of 

 moisture. This method of drying yields products which usually 

 contain a slight excess of sulphuric acid. If however the points of 

 contact between the salt to be dried and the absorbent earth be re- 

 newed from time to time, and the absorption goes on for several 

 months, compounds of sufficient purity to remove all doubts of their 

 true composition may be obtained. 



One hundred parts of the sulphate of antimony, obtained by com- 

 mon sulphuric acid and oxychloride of antimony, gave — 



Sulphuric acid 51*9 



Oxide of antimony (by carbonate of ammonia) .... 50*2 

 The composition of this salt is therefore — 



4S03 2000 51-2 



Sb^O* 1912 48-8 



3912 100-0 



Another specimen gave 53* 1 of sulphuric acid, and 44'3 of oxide of 

 antimony. 



Another sulphate of antimony was obtained in the form of small 

 brilliant crystals, by treating sesquioxide of antimony with Nord- 

 hausen sulphuric acid. After remaining ten months on the dried 

 clay, it gave — 



Sesquioxide of antimony .... 63"0 643 



Sulphuric acid 37"1 35*0 



The formula 2S03, Sb® O^ gives 65 "6 oxide of antimony and 34*4 

 sulphuric acid. 



Mixtures of these salts in different proportions were also obtained ; 



