Change in blue vegetable Colours Ly metallic Salts. 278 
Now, 3A + 8B + dC, is the excess of the angles of the spherical 
triangle above those of the plane triangle, or above two right 
angles ; and — is the area of the spherical triangle on the sphere 
whose radius is unit; and, by the well known theorem of Albert 
Girard, these quantities are equal. Wherefore 
3A + 0B +8C—— =0; 
consequently, 
(A — san (tan A+ tanB + tan C)= 0. 
Because A+ B + C = 180, tan C = — tan (A + B); therefore, 
tan A+ tan B + tanC = tan A + tan B — tan (A+ 5B), a 
quantity that in no circumstances can be equal to zero. ~Where- 
fore 
tA — = = 0; 
and hence, by equat. (4), 
5 
oA = G2? 
s 
eh= 3,2? 
C= 
Consequently, 
= Brey 7) 3 ? 
i ahigl'h 3A+43B+43C 
BB tagmsr ee? iol maniialnoe? 
luotay Ss av __ BA43B42C 
C=C- 5 = C-— 
Jivory. 
LXII. On the Change of Colour in Blue vegetable Colours by 
metallic Salts. By Mr. J. Murray. 
W: had rested quietly in the belief that the relations of acids 
and alkalis to vegetable colours were uniform ; that the first 
class of bodies turned vegetable blues to red, or restored the ori- 
ginal tint obliterated by an alkali; and that the second class, or 
alkalis, restored the blue colour changed to red hy acids, or 
deepened the yellow and red obtained from turmeric, Brasil wood, 
&c. into brown. It was at length discovered that boracic acid 
produced the same effect on turmeric as alkalis would do, and I 
further find that on tincture of cabbage, and syrup of violets, this 
peculiar characteristic is still maintained. 
Vol. 58. No, 282. Oct, 1821, . M m In 
