Deposits in Metastable Inorganic Hydrosols. 



31 



detected, and it would seem probable that the coarser fibres also arise in 

 this way from at first almost ultramicroscopic rows of granules passing out 

 of solution and joining up to form delicate fibrils. These delicate fibrils then 

 thicken up and become more obvious. Looking at the most delicate fibrils 

 actually visible, the eye so slowly takes up the details, and one becomes so 

 gradually conscious of the ramifications, that a deceitful impression is easily 

 obtained, that the structures are actually growing under the eye. But on no 

 occasion could I be certain that I had observed actual growth of a network. 



A considerable number of observations were taken to determine whether 

 there was any growth at the ends of the coarser fibres, but none could be 

 detected. In many cases where slide and coverslip preparations were pre- 

 served for some weeks, there did, however, appear to be an increase in the 

 growths, and appearances were observed of growths which certainly were 

 characteristic and well developed, and had not been seen on earlier examina- 

 tions of the same preparation. Often, with this pair of colloids, transition 

 stages in the formation of membranes from fibres are to be seen, as is 

 illustrated, for example, on the right-hand side of the lowest photograph in 

 fig. 1. The appearances given by this method of mixing two opposite colloids 

 are exquisitely beautiful and often intricate in design, although they are 

 produced so rapidly. 



Also it is important to stress the point that there can be here no con- 

 tamination eifect with adventitious living organisms. Two colloidal solutions 

 are taken, one of a positive, the other of a negative colloid, each solution is 

 examined carefully by the microscope and found to be clear and free from 

 growths, the two are carefully mixed, and there, in a period of a few minutes, 

 are the most delicate and intricately interlaced patterns of long and branching 

 fibrils, as well as growths of coarse fibres. 



The next pair of colloidal solutions investigated were ferric hydrate and 

 " colloidal sulphur « " prepared as described by Quincke (Joe. cit.). The 

 colloidal sulphur « was obtained by taking distilled water previously sterilised 

 by boiling and allowing it to cool. Two portions of the cooled sterile water 

 were taken and saturated respectively with sulphur dioxide and hydrogen 

 sulphide ; then to 20 volumes of the sulphuretted hydrogen water was 

 added one volume of the sulphurous acid solution. The result at once is a 

 fine colloidal suspension, or solution, of sulphur particles. This shows micro- 

 scopically a multitude of fine round granules all in rapid Brownian movement ; 

 on standing for about two days the particles show a tendency to grow together 

 into fine coccal-like chains. 



The solution may be diluted without precipitating and also may be boiled, 

 it may even be autoclaved at 110° C. for a few minutes with only partial 



