384 Scientific Intelligence. [Nov. 



Acetic acid 22 



Protoxide of lead 59 



Water 19 



100 



I consider the agreement as sufficiently near to leave no doubt 

 respecting the constitution of the salt ; so that it is composed of 

 5 atoms oxide of lead, 4 atoms acetic acid, and 19 atoms water. 



VIII. Remarkable Double Rainbow. By Mr. Macome. 



(To Dr. Thomson.) 

 DEAR SIR, Paishy, Sept. 7, 1819. 



The afternoon of the oth current was distinguished in this 

 neighbourhood by frequent and very brilliant exhibitions of the 

 rainbow. One of these, which happened about five o'clock, 

 attracted my particular notice from an appearance which it dis- 

 played, which to me was uncommon. The lower half of the 

 spectrum, commencing with the green rays, was distinctly 

 repeated in the regular and usual succession of the colours. 

 There was no interval of space between the usual rainbow and 

 this novel accession to it ; nor did the breadth of the spectrum 

 with this addition appear to me to be much increased beyond its 

 usual size. A dense cloud, or rather a descending shower, soon 

 interposed, and took from my view this curious phenomenon. 

 The secondary bow, with its inverted colours, was visible along 

 with the primary. The arch of either did not extend far beyond 

 the zenith, and it was the southern limb of the primary that exhi- 

 bited the appearance above stated. It would gratify me much 

 to inform me of any writer who has taken notice of any similar 

 appearance. Excuse this trouble from, dear Sir, 



Your obedient servant, 



A. Macome. 



IX. Octahedral Iron Ore. 



M. Robiquet made use of octahedral crystals of oxide of iron 

 extracted from a steatitic rock of Corsica, in the fonnation of 

 peroxide of iron ; but the colour of the oxide which he obtained 

 was bad, resembling that of rust. This led him to suspect the 

 presence of titanium in it. He dissolved a quantity of the ore in 

 muriatic acid, and evaporated the solution to dryness. On 

 redissolving the salt in water, a white insoluble powder remained, 

 which, when heated to redness with a sufficient quantity of car- 

 bonate of potash, became soluble in acids, and exhibited all the 

 characters of oxide of titanium. He extracted about six per 

 cent, of this oxide from the octahedral ore which he examined. 

 ■ — (Journal de Pharmacie, 1819, June, p. 265.) 



