This section is from the book "The Boy Mechanic Vol. 2 1000 Things for Boys to Do", by Popular Mechanics Co.. Also available from Amazon: The Boy Mechanic, Vol2: 1000 Things for Boys to Do.
One of the first lessons given a student in chemistry is how to mix sulphuric acid with water. This would naturally be supposed to be very easy, yet, if it is not done right, it will surely result in injury to the person doing the mixing.
The specific gravity of sulphuric acid is 1.849 and, on account of its chemical attraction to water, great heat is set up or generated when the two are being mixed. If the acid is put into a jar and the water poured onto it, they will be temporarily separated, as the heavy acid will remain at the bottom, the chemical reaction taking place on the dividing line only. This soon generates heat which rapidly increases until steam is formed. Then the water boils over and finally becomes a bubbling volcano which readily ejects the contents of the jar. As the mixture at this moment is very hot, bad burns will be the result, which are aggravated by the biting of the acid; and clothing or anything that it comes in contact with will be ruined or badly damaged. Always remember this caution: add the acid to the water.
The following is the proper way to proceed in mixing sulphuric acid as well as other acids of lighter weight. Place the water in a jar and pour the acid in, a little at a time, stirring the mixture with a wooden stick. The mixing process will always heat the solution, which in many instances, must be allowed to cool before using.