1873.] On a Method of viewing the Solar Prominences. 127 



Theory. I. II. Mean. 



(C 7 H 12 N 3 3 ) 2 = 372 79-49 



S0 4 = _96 20-51 20-65 20-72 20-69 



468 100-00 



The formula of this salt would therefore appear to be 

 [0, (CH 3 ) (NH 2 ) (NH), (HO),], S0 4 + H, O. 



Amido-diimido-orcin nitrate is prepared, like the sulphate, by adding a 

 slight excess of nitric acid to a moderately strong solution of the acetate 

 and washing the precipitate with alcohol. It closely resembles the sul- 

 phate in appearance, but is much more soluble in water. When heated 

 with excess of nitric acid it is decomposed, yielding a yellow solution, 

 which, on being evaporated, leaves a mixture of oxalic acid and an amor- 

 phous yellow substance. 



Amido-diimido-orcin acetate. — Amido-diimido-orcin dissolves readily in 

 acetic acid ; and on carefully evaporating the solution at a low tempera- 

 tare, the acetate is obtained in ill-defined crystalline plates having a purple 

 iridescence. It is readily soluble in cold water, but only slightly soluble 

 in glacial acetic acid. 



Amido-diimido-orcin oxalate. — Very slightly soluble purple scales ob- 

 tained by precipitating a solution of the acetate with oxalic acid. 



Amido-diimido-orcin picrate. — On adding a solution of picric acid to a 

 dilute solution of amido-diimido-orcin acetate and washing the precipitate 

 with alcohol, the picrate is obtained in iridescent green needles and plates. 

 It is insoluble in alcohol, and but slightly soluble in water. 



I cannot conclude this paper without acknowledging the very efficient 

 aid I have received from my assistant, Mr. Charles Edward Groves, in 

 conducting this investigation. 



II. " Note on the Wide-slit Method of viewing the Solar Promi- 

 nences." By William Huggins, D.C.L., LL.D., F.R.S. 

 Received November 21, 1872. 



When editing the English translation of Schellen's ' Spectrum Ana- 

 lysis,' I discovered that the short account of the method of viewing the 

 forms of the solar prominences by means of a wide slit, which I had the 

 honour of presenting to the Royal Society on February 16, 1869*, does 

 not agree exactly in one respect with the account of the observation of 

 February 13 as it was entered at the time in my observatory book. The 

 short note was written at the suggestion of a friend during a Committee 

 held in the Royal Society's Apartments, and, as the concluding words 

 show, was intended to be followed by a more detailed account of the 

 method of observation. The point in question relates to the position of 

 a second slit which was used to screen the eye from every part of the 



* Proc. Rov. Soc. vol. xvii. p. 302. 



