4K^ On a Deposit found in the Waters at Lucca. [March, 



ipaldi or hot baths, eject in a considerable quantity a substance 

 that produces a deposit of a brownish-yellow hue. Having col- 

 lected various quantities of this deposit, and having submitted 

 it to chemical experiments, I have discovered it to be a compound 

 of oxide of iron and sihca : not having a balance sufficiently 

 Accurate, it was impossible for me to ascertain v/ith precision 

 t^xe exact proportions : in the single experiment, however, that I 

 ^ade for this purpose, the oxide of iron was to the silica in the 

 IH'oportion of 4 to 3. 



It is extremely probable that the oxide of iron and the silica 

 bad been dissolved together in the water, and deposited at the 

 eame time, because the silica being separated from the oxide by 

 ineans of a weak acid, it appears to resemble gelatine, and 

 •because the deposit, when examined in its natural state, wae 

 found to be uniform in its substance, even when looked at 

 through a lens. 



Although the oxide of iron, when first discovered, proves to 

 be peroxide, it is nevertheless very probable that it exists in 

 the water in the form of protoxide, or that it is converted into 

 peroxide by the action of the air which is dissolved in the 

 ;ivafeer. The probability of this opinion is further confirmed by 

 the circumstance, that the colour of the water is not changed 

 l>y the addition of the triple prussiate of iron, nor by that of 

 gallic acid, it being well known that protoxides generally have a 

 greater disposition than peroxides. 



The analogy which I established some time since, during my 

 researches as to the decomposition of alkalies and earths, 

 43etween the base of silica and that of boracic acid, and the facts 

 ^described by MM. Smithson and BerzeUus, furnish reasons for 

 classing silica among the acids ; and it seems probable that the 

 joxide of iron and the silica undergo a real chemical combination 

 in the warm water, and that they separate from it in conse- 

 quence of its cooling after issuing from the mountain. 



When the deposit is obtained from its diffused state in water, 

 it contains no other substances than oxide of iron and silica ; when 

 it is taken from the bottom of the waters, carbonate of hme and 

 sand may be observed mixed with it. These two substances are, 

 however, evidently extraneous. From many experiments which 

 I made I am convinced that after it has quitted its source, the 

 water yields no deposit whatever ; but it appears certain that the 

 water, which, on rising from the spring, possesses a temperature 

 of 112°, must be much warmer within the mountain, and that 

 <jonsequently its solvent power must there be much greater. 



When a considerable quantity of it is evaporated, a small por- 

 tion of silica and oxide of iron is found, a discovery that had 

 been made by Signor Battista Tessandori; and I have ascer- 

 tained by experiments that these substances are obtained in the 

 isame state, and nearly in the same quantity, in which I have 

 stated them to be discovered in the brownish-yellow deposit. 



