In determining the strength of an acid or alkai, there is sometimes confusion between the theoretical and actual concentration of the solutions which can lead to over specifying the body material and diaphragm most suited to the application.

The table below attempts to clarify the relationship between the Strength (in % by weight) and specific Gravity.

For example a request for 100% Hydrochloric Acid is often received.

From the table it can be seen that the maximum strength that can be obtained is 40% or an S.G. of 1.1980.

We always assume that when asked for 100% Hydrochloric acid the application is actual for the acid at an S.G. of 1.180.

Similarly 100% Sulphuric Acid normally is considered to be a strength of 98% % by weight, however sulphuric acid can be obtained at stengths of 100% and over which is in the ‘Oleum state’ and requires careful material application based on accepted corrosion critria.