This salt (sodium pyroborate, Na2B407,10H20) is alkaline in reaction, and behaves as an alkali when added to aqueous solutions of alkaloidal salts, but the addition of a few drops of glycerin prevents precipitation. It does not behave as such, however, when an alkaline carbonate is added to an aqueous solution of borax, but solutions of borax in glycerin or honey effervesce when a carbonate is added. For example, the following lotion, typical of many which could be reproduced, burst the bottle a short time after it was dispensed, owing to evolution of carbonic-acid gas:

The change is due to interaction between the borax and glycerin. When borax and glycerin are heated together in molecular proportions, a decomposition, represented by the following equation, takes place:

Glycerol-borin ('boroglyceride ') and water interact thus:

Therefore, if the water resulting from the first reaction is not driven off by heat, the resulting glycerin (as in the case of glycerin, boracis, B.P.) contains free boric acid, and when a bicarbonate is added effervescence immediately ensues. The two reactions also take place in the lotion above mentioned, and in all similar lotions containing glycerin, borax, sodium bicarbonate, and water. The reaction is one common to poly-hydric alcohols, of which glycerin, dextrose (in honey), and mannite (in manna) are the most familiar representatives; consequently, if any of these occur along with borax and a carbonate, effervescence is inevitable and should be completed by heating before the solutions are dispensed. The modus operandi for the prescription quoted is: Mix the borax with the glycerin and 2 ounces of rose-water, heat, and add the bicarbonate, stirring until effervescence ceases. When cold add the carbolic acid dissolved in the rest of the water, and make up. The following are additional peculiarities:

Without the glycerin No. I. is a clear solution, with it aprecipitate of boric acid is obtained. On heating the mixture the acid dissolves (in the glycerin, doubtless) and is not re-precipitated on cooling. No. II. yields a precipitate of aluminium borate (3AI2O3.2B2O3) with alkaline sulphate. Zinc sulphate gr. viij. and borax gr. x. in an ounce of water give a white precipitate, but not if a few drops of glycerin is added.

A tablespoonful to be mixed with a cupful of warm water for use as a spray for the throat.

On diluting this with hard water a light voluminous precipitate of aluminium tannate, induced by lime salts, is formed, but not so when distilled or soft water is used.

Boroglyceride when treated with water decomposes into boric acid and glycerin, and if sufficient solvent is not present, boric acid is precipitated (see p. 344).