of Chemical Equivalents, ^5 
ing 185,5 red oxide of mercury, or would make 91,5 muriate 
of ammonia, composed of 6 muriatic gas (or hydromuriatic 
acid) and 29,5 ammonia. The scale shews also, that for the 
purpose of obtaining the whole of the acid in distillation the 
quantity of oil of vitriol required is nearly 84, and that the 
residuum of this distillation would be 122 dry sulphate of 
soda, from which might be obtained, by crystallization, 277 
oi"' Glauber salt containing 155 water of crystallization. 
These and many more such answers appear at once by bare 
inspection, as soon as the weight of any substance intended 
for examination is made by motion of the slider correctly to 
correspond with its place in the adjacent column. 
With respect to the method of laying down the divisions of 
this scale, those who are accustomed to the use of other slid- 
ing-rules, and are practically acquainted with their properties, 
will recognise upon the slider itself the common Gunter's 
line of numbers, (as it is termed) and will be satisfied that 
the results which it gives are the same that would be obtained 
by arithmetical computation. 
Those who are acquainted with the doctrine of ratios, and 
with the use of logarithms as measures of ratios, will under- 
stand the principle on which this scale is founded, and will 
not need to be told that all the divisions are loffometric. and 
consequently that the mechanical addition and subtraction of 
ratios here performed by juxta-position, corresponds in effect 
to the multiplication and division of the numbers by which 
those ratios are expressed in common arithmetical notation. 
To others who are not equally conversant with the nature 
of logarithms, and consequently have not so correct a concep- 
tion of the magnitudes of ratios, some further explanation of 
