To obtain hæmateïn in the pure state it is then only necessary to add sufficient acetic acid to decompose the hæmateïn ammonia compound. Hæmateïn separates as dark violet crystals, which readily dissolve in water and alcohol; its aqueous solution gives blue precipitates with the majority of the metallic salts. This behaviour of hæmatoxylin towards ammonia explains the increase in colouring power of logwood, which has been exposed for a long time to the action of the air in the rasped state. Through the action of the ammonia in the air a larger quantity of the hæmateïn ammonia compound has been formed. It has been proposed to facilitate the formation of this ammonia compound by moistening rasped logwood with a very dilute glue solution and allowing it to lie in the air. This process can only have the object of utilising in the formation of hæmateïn the ammonia resulting from the decomposition of the glue, but in this decomposition deep-seated reactions occur, which might affect the hæmateïn itself. It thus appears more suitable to effect the formation of hæmateïn by the direct use of ammonia. This can be done with little cost by watering heaps of rasped logwood with ammonia and repeatedly shovelling about the wood so that it comes into contact with the air. The author has found that the conversion of hæmatoxylin to hæmateïn is very complete in this process; care should be taken not to make the layer of rasped wood too deep, and to take its temperature frequently. In the transformation of hæmatoxylin to hæmateïn the temperature rises, the rise might be injurious if it proceeded too far. Thus if the temperature of the interior of the heap is found to be high the wood should be turned over. The solution of the logwood colouring matter produces handsome lakes, all of which have, however, the inconvenient property of acquiring an ugly grey colour on long standing. The finest and most durable of the logwood lakes is known as violet lake, which is made with alumina salts. The best result is obtained when a solution of aluminium acetate, obtained by precipitating alum with lead acetate, is mixed with a logwood decoction or a solution of logwood extract. The precipitate is pale or deep violet according to the amount of aluminium salt added. After drying to a certain point at a gentle heat it can be mixed with gum solution to a paste, which is then completely dried.