Hypochlorite of soda was discovered by Berthollet in 1788, and its antiseptic properties have been known for a long time. Labarraque gained great renown by-embalming, by the aid of his liquor, the corpse of Louis XVI11., which was so extremely decomposed that no one could come near it. But neither Labarraque's solution nor eau de Javel can be used with safety in surgery. One of the essential conditions of the sterilisation of wounds is, as is well known, the employment of a substance which, in a given degree of concentration, can be applied for a long period to wounds without irritating them. This is the reason why it is impossible to use commercial hypochlorites, whose content of hypochlorite is extremely variable and which contain free alkali. The proportion of alkali contained in eau de Javel and Labarraque's liquor is great enough to produce solution of the skin, if the contact be sufficiently prolonged.

I. Dakin's Technique

That is why Dakin sought the means of obtaining a solution deprived of free caustic alkali, and whose content of hypochlorite must not vary beyond the limits of 0.45 and 0.50 per cent. Later experiments by Daufresne showed that below 0.45 per cent. the solution is insufficiently active, whilst above 0.5 per cent. it is irritating. At the time of his communication to the Academie des Sciences, Dakin gave a method of preparation of this solution which enabled it to be made with the simplest appliances, without chemical knowledge.

"140 grammes of anhydrous carbonate of soda, or 400 grammes of the crystallised salt, are dissolved in 10 litres of ordinary water, and 200 grammes of chloride of lime 1 of good quality are added to it. The mixture is well shaken, and at the end of half an hour the clear liquid is siphoned off and filtered through cotton. To the filtrate are added 40 grammes of boric acid, and the solution thus obtained may be used at once; it does not colour phtalein in suspension in water." 2

This very simple mode of preparation was easy to execute, a great advantage for hospitals at the front. But experience in its use has brought to light several inconveniences, which have been studied by Daufresne. One of the products used in its preparation, chloride of lime, being of very variable composition, its content of active chlorine might vary from the normal to double the amount. Under the influence of humidity it forms compact masses, which, when agitated with the solution of carbonate of soda, are incompletely broken up, and only yield a portion of their hypochlorite. These are the reasons why defective solutions have sometimes been obtained while following conscientiously the procedure just described.

1 The salt referred to is of course not calcium chloride, but calcium chlorate, or chlorinated lime, universally known as chloride of lime (Tr.) 2 Dakin, Presse Midicale, loc. cit.

On the other hand, Daufresne was led to attribute certain irritation phenomena to the boric acid employed to neutralise the solution. In fact, without being able to give an exact account of the chemical reactions which enter into the change, every time the quantity of boric acid used to arrive at non-coloration in the phtalein test exceeds 4 grammes per litre, the solution becomes unstable and painful.

Besides, the solutions of hypochlorite prepared with boric acid, even in correct quantity, keep badly.