Dr F. Penny on the Valuation of Indigo, 285 



numerous vases and other ornamental vessels usually found 

 in drawing rooms would be found available. 



4. Rain.— The greatest quantity of rain which fell in one 

 day during the year was 1*37 inches, on the 24th August ; 

 this is one-third more than fell during the entire months of 

 March and April. 



5. Wind. — It will be seen from the table of the direction of 

 the wind, that it blows at 9 A.M. 2J times more frequently 

 from the W to S. arc than from the E. to N. arc ; the num- 

 bers being 199 days from the SW. arc, and 90 days from the 

 NE, arc, and that the NE. winds are the least prevalent 

 throughout the year, occurring principally in the spring and 

 autumn. 



On the Valuation of Indigo. By Dr Frederick Penny, 

 F.C.S., Professor of Chemistry in the Andersonian Uni- 

 versity, Glasgow. 



Several methods have been employed for estimating the 

 comparative value of commercial indigo. 



The colorimetric processes with chlorine, proposed by Ber- 

 thollet, and first practically applied by Descroizilles, have 

 been most extensively tried, and have been fully described by 

 Berzelius,* Chevreul,f Schlumberger,J Schubart,§ Persoz, || 

 and others. In these processes chlorine-water or bleaching- 

 powder was used as the source of the chlorine. 



Bolley % has proposed chlorate of potash and hydrochloric 

 acid as the source of chlorine, and has reported very favour- 

 ably of the results obtained by operating upon specimens of 

 various qualities. 



Some chemists consider that the only method of accurately 

 determining the value of this article consists in removing the 



* Traite de Chimie. t Le9ons de Chimie appliquee a la Teinture. 



X Bullet, de la Soc. Industr. xv. 277. § Tech. Chimie. 



|| Traite de PImpression des Tissus. «[ Ann. Ch. Pharm. 1850, 



VOL. LIV. NO. CVI1I. — APRIL 1853. U 



