486 PHILOSOPHICAL TRANSACTIONS. [aNNO 1 700. 



rations In the fermentation of tlie liquors in the plants, &c. of the wine, and 

 also in the distillation, which alterations the naineral acid lias not received. 

 The vegetable acid by that subtility of particles is able to impregnate a greater 

 quantity of liquor than the same quantity of mineral acid, and by that it is more 

 easily raised by the fire than the others. 



By these observations M. Homberg makes evident the reason of some cases 

 difficult to be explained without them ; as it is well known that one ounce of 

 aquaregia, compounded with the spirit of nitre and the ammoniac salt, dissolves 

 twice more gold than an ounce of the spirit of salt can do. Chemists attribute 

 that effect to the softness of the points of one acid, and to the hardness of the 

 other ; when these observations show evidently that the spirit of nitre contains 

 twice more acid salt than the like volume of spirit of salt, and points out at the 

 same time the true cause of this effect.* 



M. Homberg also showed how, by the comparison of these two tables, we 

 may know the quantity of acid salt contained in an acid spirit, in the following 

 manner : he took an acid spirit, as spirit of nitre, he weighed it by his areo- 

 meter, and at the same time he weighed also distilled water, (for the weight of 

 the phlegm contained in the acid spirits is proportionable to the weight of the 

 distilled water,) then he consulted the tables, where he saw that the bulk of 

 spirit of nitre compared with the like bulk of distilled water has given a certain 

 quantity of acid salt for each ounce ; and from thence he concludes, that the 

 bulk of other spirit of nitre, of which the weight is known, compared with the 

 like bulk of water, shall give a determined quantity of acid salt, which will be 

 obtained by the computation of the relations of the weights of those spirits, 

 with the weights of the like bulks of distilled water, by concluding from 

 them, and from the known product of acid salt for the unknown product of 

 the same. 



An unusual Parhelion and Halo. By Mr. Stephen Gray. N° 262, p. 535. 



April the 7th, iSgg, between 4 and 5 o'clock, I perceived the following 

 phaenomena ; There appeared on each side the sun a parhelion, connected by a 

 halo of the usual diameter ; tliey had each of them a tail of a whitish colour ; 

 extended opposite to the sun, of about 15 or 20 degrees in length; the upper 

 part of the halo was touched by the arch of a circle, whose ends were turned 

 towards the zenith ; it had the colours of the iris but faintly. Between this and 



* Modern chemists explain this phenomenon differently. They suppose that in the preparalioa 

 of aqua regia as above described, the nitric acid (spirit of nitre) imparts a quantity of oxygen to the 

 muriatic acid contained in the sal ammoniac, thereby converting a portion of it Into oxymuriatic 

 acid ; in which state this acid acts readily upon gold. 



