——. ee 
On the Artificial Formation of Minerals. 299 
_ The results of Professor Graham’s researches on the dif- 
fusion of liquids, suggested to him the idea that by means of 
this process a very gradual precipitation might be effected, 
which would be eminently favourable to the production of 
insoluble or sparingly soluble substances in a crystalline 
form. 
The first experiment, directed to the production of inso- 
luble lead salts, was arranged in the following manner :— 
Powdered nitrate of lead was introduced into a tall cylin- 
drical glass and covered with water; chromate of potash 
containing carbonate and sulphate was placed in a similar 
glass with water, and both were then immersed in a large 
vessel of water. The saline solutions formed at the bottom 
of the glass cylinders diffused slowly upwards, and after 
some months, the water in the large vessel was found to 
contain nitrate of lead. There was then formed upon the 
outer edge of the second cylinder a yellow amorphous de- 
posit, which gradually extended towards the inner edge and 
assumed a darker colour. Upon this amorphous deposit, 
small patches of a bright purple red colour appeared after a 
time and rapidly increased to little warty protuberances, and 
finally formed a ring extending downwards in a horizontal 
zone round the inner side of the cylinder. The other por- 
tion of the cylinder became covered with a reddish film, 
which, after a few days, was seen to consist of small crys- 
tals. These increased rapidly in size, forming concentric 
groups of acicular crystals of a bright red colour. Some 
attained a length of four or five millimetres, and then fell to 
the bottom of the liquid. The crystals had adamantine 
lustre, and corresponded in crystalline form as well as in 
every other particular with native lehmannite (PbO, CrO,). 
Upon the dark red ring rhombic plates of a cochineal 
colour were formed and grouped together in branches, and 
agreeing in characters with phcnicite (3 PbO, 2 CrO,). 
_ The formation of these two compounds took place in such a 
manner, that near the mouth of the cylinder there was a zone 
of pheenicite only ; lower down, crystals of both compounds 
were associated, while below this point there was another 
zone of lehmannite only ; and when the liquid was tested with 
