180. Sulphuric acid of 6o° Beaume, or 1.76 sp. gr., containing, according to Ure, 69.31 per cent of "dry acid," costs four cents per pound in San Francisco. One pound of this acid is equal to 1.06 pounds of acid of 63° Beaume, or 1.71 sp. gr., containing 65.25 per cent of dry acid, and costing 2 1/2 cents per pound. From this it is evident that the weaker acid is the cheaper to use, unless freight costs 15 cents per pound. (Double freight is charged on acid by the Railroad Companies.) For example: 1 lb. of acid of 66°......... 4 cents.

1 lb. freight............... 15------------19 cents.

1.06 lbs. of acid of 63°. . . 2.65 cents. 1.06 lbs. freight at 15 cts. . 15.9 ------------ 18.55 "

Taking into consideration the freight on the carboys, which must be paid both ways if they are returned, thoug,h not equally, an addition of about 30 per cent must be made to the weight on which double freight must be paid, and about 20 per cent of ordinary freight, or 10 per cent of the first addition, making the cost of the acids respectively:

Strong acid per lb. as above.. 19. cents.

Freight on carboy going......4.5 "

" " returning.. . .0.45------23.95 cents.

Weak acid as above, 1.06 lbs. .. 18.55 cents.

Freight on carboy going..... 4.77 "

" " returning.. . 0.47 -------23.79 cents.

The carboys are charged for at the rate of $2.25 each, and if not returned their cost must be added to that of the acid. This makes an inappreciable difference in the relative cost of the two grades. Acid can be bought and freighted more cheaply if a carload is taken at once.