MTJREXIDE 377 



an operation, delicate and complex, even as a laboratory process, made available on 

 an industrial scale. Those who had only* seen murexide adorning as a rarity the 

 shelves of a museum, might well be astonished when they found it by hundredweights 

 in the market, nearly equalling in purity the laboratory product itself, and sold at a 

 price almost incredibly low. 



The reporter had the good fortune to be a student in Professor Liebig's laboratory 

 at the time, when, together with Professor Wohler, he carried on those researches upon 

 uric acid which became celebrated for the brilliant light they threw upon the nature 

 and composition of murexide. He has thus had many opportunities of witnessing the 

 difficulties which arose in the preparation of the substance ; and he can record, as he 

 shared, the triumph which the whole laboratory felt when a few grammes of it were 

 first obtained in a state of purity. 



Murexide has the formula C 8 H'N 6 6 , and has been considered by some as pur- 

 purate of ammonium. The acid of this salt cannot, however, be isolated. As soon as 

 it is set free by means of a stronger acid, it is immediately decomposed into other 

 products, murexan, alloxan, &c. 



Preparation of Murexide. The preparation of murexide involves two distinct 

 operations, viz.: 1. The extraction and purification of uric acid. 2. The transfor- 

 mation of uric acid into murexide. 



Sources of Uric Acid. Uric acid is found in the excrements of serpents and birds, 

 and in guano, as urate of ammonium. The excrements of serpents contain almost 

 pure uric _acid, partly combined with ammonium, partly free. The supply of these 

 materials is, however, too limited to serve for any other than laboratory experiments. 



Almost all the uric acid used in the arts is derived from guano. According to the 

 process patented by Mr. Brooman, the guano is extracted by means of hot dilute 

 hydrochloric acid, which dissolves out the carbonates, oxalates, and phosphates of 

 ammonium, calcium, magnesium, &c. The insoluble residue consists of uric acid, 

 mixed with sand, clay, sulphate of calcium, albumen, mucus, &c. It is treated with 

 fresh quantities of hot hydrochloric acid, washed, drained, and dried. It may then 

 be employed directly for the preparation of murexide. 



But if a purer uric acid be required, it may be obtained by dissolving the crude acid 

 in a boiling solution of dilute caustic potash, and precipitating the clear solution with 

 an acid. The uric acid is thus obtained almost pure, and may be filtered, washed, 

 and dried. 



The uric acid can also be dissolved in rather concentrated sulphuric acid, heated to 

 60 to 80 C., and then precipitated by the addition of water, filtered, washed, and 

 dried. 100 parts of good guano yield from two and a half to three parts of uric acid. 



Transformation of Uric Acid into Murexide. For this purpose the uric acid is first 

 dissolved in cold nitric acid, which is placed, for this purpose, in earthenware pots of 

 from four to five litres capacity, and has the uric acid gradually added to it in small 

 quantities ; each portion being allowed to dissolve entirely before a fresh quantity is 

 introduced. 



This operation takes from ten to twelve hours, and yields a dark brown liquid, 

 consisting chiefly of nitrate of urea, alloxan, and alloxantine. These last two substances 

 frequently form a crystalline crust on the surface of the liquid, and their simultaneous 

 presence forms one of the most favourable conditions for the abundant formation of 

 murexide. 



The liquid thus obtained is treated in one or other of the two following modes : 



1. When it is desired to obtain purpurateof sodium, it is simply diluted with water, 

 mixed with carbonate of sodium, and heated. 



2. When, on the other hand, purpurate of ammonium, or murexide is required, 

 carbonate of ammonium is added. 



The liquid thus obtained is evaporated in glazed vessels of considerable size, care 

 being taken not to raise the temperature beyond 80 C., and not to operate upon too 

 much liquid at one time. In proportion as the liquid becomes more concentrated and 

 pasty, ammonia, set free by the decomposition of the nitrate of urea or urea alone, 

 reacts in its nascent condition, upon the alloxan and alloxantine, and forms murexide, 

 which appears on cooling as a brownish-red or violet substance, sometimes of a greenish 

 tint. _ This constitutes the purple carmine of Mr. Brooman. 



It is, however, better to employ ammonia, or its carbonate, added in small quantities 

 nt a time to the nitric solution, till the acid liquid is neutral or slightly alkaline, which 

 reaction it should permanently retain. This liquid is then heated to about 60 to 77 

 C., and yields, on cooling, crystals of murexide* The mother-liquid is again heated 

 with small quantities of ammonia and cooled ; when a fresh crop of crystals of mttrexido 

 is obtained. 



Crystallised Murexide. During the last few years the dyers and printers have 

 gradually abandoned the use of pastes of murexide, in order to employ it solely in the 



