604f Intelligence and Miscellaneous Articles, 



made -with the centre yards of each scale. It appears that 215 

 comparisons were made on nine several days by three different per- 

 sons ; and the mean of the whole showed that the centre yard of 

 the Neapolitan scale was longer than the standard yard of the So- 

 ciety's scale, by '002680 of an inch : the greatest differences from 

 the mean being +'000520 and —-000365 of an inch. This new 

 scale is marked No. 6 ; it being the sixth scale of this construction 

 that has been made. 



On the Difference of Longitude between the Observatories of 

 Madras and the Cape of Good Hope, deduced from Moon-culmina- 

 ting stars. By T. Maclear, Esq. 



The observations extend from February 19, 1834, to October 10, 

 1837, both inclusive, and contain all the corresponding observations 

 within that period, except two which appear to be erroneous ; and 

 amount to seventy in number. Of these, only three were of the 

 second limb. The result of the whole shows that the difference of 

 longitude is 4^ 7"° P"56, with a probable error of + 0'-53. 



LXXXII. Intelligence and Miscellaneotis Articles. 



ON THE LIMIT TOTHE ACTION OF CERTAIN CHEMICAL REAGENTS. 



MP. HARTING ha\ang examined the action of certain chemi- 

 • cal reagents, has given the following statement as the result. 

 1. The sensibility of starch as a reagent for iodine. 

 Iodide of potassium slightly acidulated with nitro-muriatic acid, 

 tested by a diluted solution of starch, gave the following results. 



1. Containing l-500dth iodine gave a black precipitate,, the upper 

 surface was brownish yellow. 



2. Containing 1-lOOOdth iodine gave nearly the same colour. 



3. Containing l-2000dth iodine gave the precipitate the same 

 colour, but the solution slightly coloured. 



4. Containing l-3000dth iodine, precipitate bluish black, the so- 

 lution nearly clear. 



5 and 6. Contaming l-4000dth to l-5000dth iodine, precipitate 

 bluish black, the solution quite clear. 



7 to 11. Containing l-10,000dth to l-40,000dth iodine, very dark 



blue. 



12 and 13. Containing l-50,000dth to l-60,000dth iodine, blue 

 with a shade of violet. 



14 and 15. Containing l-80,000dth to l-100,000dth iodine, the 

 upper stratum violet blue, the under stratum violet. 



16. Containing l-120,000dth iodine, the upper stratum violet, 

 the under stratum rose-colour. 



17. Containing 1-150, OOOdth iodine, the whole precipitate rose- 

 colour, with a shade of violet. 



18 and 19. Containing l-200,000dth to l-250,000dth iodine, 

 rose-colour, the upper surface only with a slight shade of violet. 



20 to 22. Containing l-300,000dth to l-400,000dth iodine, tlie 

 whole precipitate of a rose-colour. 



