Dr. Ure on Muriatic Acid, &c. 291 



and secondly, because, though it was a convenient column for 

 finding by inspection the increase of weight which any salifiable 

 base would acquire by saturation with the liquid acid, yet that 

 convenience may be obtained by the following simple calcula- 

 tion. Since the prime equivalent of chlorine is to that of the 

 supposed dry muriatic acid, in the ratio of 45 to 35, or 9 to 7 ; 

 if we multiply the number opposite to the given specific gravity, 

 in the chlorine column, by 9, and divide by 7, we shall have the 

 relative quantity of the^xa6/e muriatic acid. 



Heretofore, several chemists have, without due consideration, 

 assumed the half sum, or arithmetical mean of the specific gra- 

 vities of two substances (water and acid, for example,) to be 

 truly the calculated mean; and on comparing the number thus 

 obtained with the experimental specific gravity of the compound, 

 they have inferred the change of volume due to chemical com- 

 bination. It is a singular fact, that the above arithmetical mean, 

 which is always greater than the rightly computed mean, (see 

 my paper on Mean Specific Gravity, in this Journal, vol. iv. 

 p. 151,) happens to give in the case of liquid muriatic acid, an 

 error in excess, very nearly equal to the actual increase of density. 

 From this curious coincidence we derive a very simple rule for 

 finding the approximate value of chlorine in the liquid acid at 

 any density. Multiply the decimal part of the number repre- 

 senting the specific gravity by 200, the product will be the chlo- 

 rine present in 100 parts. Thus, the specific gravity is 1.0437, 

 what is the quantity /jer cent, of chlorine ? 0.0437 x 200=8.74. 

 Now the tabular number is 8.729. The sp. gravity being 1.059, 

 what is the value of the chlorine in 100 parts } 0.059 x 200= 

 1 1.8. The table has 1 1.9. Towards the head of the table this 

 rule gives a slight error in excess ; and towards the foot an 

 equally slight error in defect, but the approximation is always 

 good enough for ordinary practice, seldom amounting to one- 

 half per cent. If to the number thus found for chorine we 

 add ^g part, the sum is the corresponding weight of muriatic 

 acid gas. 



