Chemistry and Physics. 467 



SCIENTIFIC INTELLIGENCE. 



I. Chemistry and Physics. 



1. A New Method for the Deter minatioji of the Faintest 

 Traces of Arsenic. — Armand Gautier, who has devoted much 

 attention to the determination of small amounts of arsenic, and 

 to the distribution of this element, has now described a very 

 simple and accurate method for determining the most minute 

 quantities of it. The method, which is particularly well adapted 

 to the examination of chlorides, while the older methods present 

 difficulties in such cases, consists in adding, under proper condi- 

 tions, specially purified ferric sulphate solution to the liquid to 

 be tested, boiling, and thus precipitating all the arsenic with the 

 basic ferric salt ; then dissolving the filtered precipitate in sul- 

 phuric acid and using the resulting solution directly in the Marsh 

 apparatus. 



The method is so delicate that 0*00 1™^ of arsenic in a liter of 

 water is entirely recovered by means of it. A sample of sea- 

 water taken at SO'^™ from the coast of Brittany, at a depth of 5™ 

 gave 0*010™^ of arsenic per liter; water from near the Azores, at 

 10, 1335 and 5943"^ depth gave 0*025, O'OIO and 0-080"^e per liter; 

 water from a salt spring at Missery gave 00 10™^ per liter; various 

 samples of common salt gave from 0*001 to 0*045"^^ in 100^, 

 while a sample of the same substance from a volcanic fissure at 

 Vesuvius gave 0*175™^ in 100^. Various reagents supposed to 

 be pure were found to contain arsenic; thus water distilled from 

 copper and glass after the addition of sodium carbonate gave 

 0*0007 and 0*001 1™^ per liter, while so-called pure ammonia-bicar- 

 bonate of soda, potassium nitrate and sulphate, etc., gave appre- 

 ciable quantities of the element. — BuUethi^ xxix, 859. h. l. w. 



2. The Influence of Small Quantities of Water in bringing 

 about Chemical Reactions between Salts. — Many experimenters 

 have investigated the influence of traces of moisture in reactions 

 between gases, but ap|)arently no one has hitherto made similar 

 experiments with solids. Perman has therefore made a number 

 of experiments in this direction, and has chosen for this purpose 

 the salts of lead and mercury mixed with salts of potassium, 

 usuall}^ the iodide, where the progress of a reaction would be 

 indicated by a change of color. Equivalent quantities of lead 

 chloride and potassium iodide were dried over strong sulphuric 

 acid and then mixed. It was found that after drying forty-eight 

 hours no visible change took place on mixing the salts, but on 

 keeping the mixture a week in a sealed flask a faint yellow 

 color appeared, which, after some months, became bright yellow. 

 Attempts were made to find how much water was necessary in 

 order to make the reaction immediately visible; the results were 

 not very concordant, but indicated that about 0*5'^^ was neces- 

 sary when 2s of potassium iodide and an equivalent quantity of 



