TEST FOR CARBONATE OF MAGNESIA.
The third test tube may be examined for carbonate of magnesia, which is found freely mixed with the water of many wells. Put aqua ammonia in this tube, and add twenty drops of a solution of phosphate of soda. A crystalline precipitate will indicate the presence of magnesium. Where carbonate of magnesia is present in considerable quantities in water, it sometimes forms along with lime a thick, porous scale; and in other cases it is apt to float on the top of the water, causing trouble by making the boiler foam. If an engine boiler has got scale formed from water free from magnesia, and goes on to a division where this impurity abounds, the magnesia will take off the old scale before it begins to form new incrustation. A few pounds of common salt put into the tender daily will have a good effect in preventing trouble with magnesia; since it forms chloride of magnesia, which is a decided preventive of lime scale.