SCIENTIFIC SUMMARY. 
385 
finds that silicic acid, precipitated from a water-glass, produces fermenta- 
tion in saccharine solutions, particularly after the addition of some tartaric 
acid, and generates the odour of beer yeast, afterwards of fruits, and 
finally of ether ; in very dilute solutions, the odour of putrid yeast 
appears. Silicic acid does not lose this property by boiling with water, or 
by repeated employment for fermenting and subsequent washing with 
water. 
The very rare metal vanadium has been found by H. Sainte-Claire 
Deville to be a frequent constituent of clay. In some researches on the 
mineral bauxite, he found that the colour which was thought to be due 
to the presence of chromium was, in reality, owing to vanadium. This 
led to a special search for this rare element, when it was found to be a 
frequent constituent of clay. It has since been found in clays from the 
neighbourhood of Paris, from Gentilly, and the refractory clay of Farges- 
les-Eaux. It seems, therefore, to be well established that vanadium 
may be found in most clays. Captain Caron has likewise found it in the 
emerald, in several natural aluminates, and in a very abundant iron ore 
found in the department of Cher. 
The universality of the presence of arsenic is receiving stronger con- 
firmation every day. C. L. Bloxam, the discoverer of perhaps the most 
delicate test for this element, has lately instituted a long series of experi- 
ments, in order to obtain sulphuric acid free from arsenic. Starting with 
the acid of commerce, which always contains arsenic, he successively tried 
distillation with chloride of sodium, passing hydrochloric acid gas through 
the boiling acid, electrolysis, fractional distillation, and distillation with 
oxydizing agents. None of these plans, however, would remove the acid. 
He then attempted to prepare the acid direct from sulphurous acid by 
passing a mixture of it and air over platinised pumice stone, but this 
yielded arsenic. Nitric oxide was then used to oxidise the sulphurous 
acid, but here arsenic was obtained from both gases. Lastly, he used 
carefully purified sulphite of soda, as a source of sulphurous acid, and a 
mixture of sulphate of iron, nitric acid, and sulphuric acid as a source 
of the nitric oxide. When these gases were prepared at low temperatures, 
the resulting sulphuric acid was at length found to be free from arsenic. 
It may be of interest to know that, amongst other bodies containing 
arsenic, common salt is included. 
Silicium, the metallic basis of rock crystal, has been obtained, in a fused 
state, by II. Sainte-Claire Deville, and also by Captain Caron. It melts 
at about the fusing point of iron, and can be got in the form of bars and 
globules. A full account of the physical properties of this substance 
would be very interesting. At present, however, no full particulars have 
been made known. 
The intensity and persistence of odour of some organo-metallic bodies 
are remarkable. One of the most striking illustrations which we have 
ever met with is afforded by a new body, tellurium-methyl , recently dis- 
covered by Dr. Max Heeren. If a small quantity of this substance is 
allowed to get on to the finger, it soon communicates a smell to the whole 
body, and in a few days is perceptible in the breath. The stench is so 
lasting, that the unfortunate chemist is shut out from society for several 
months. 
