190 J. H. Bill—Decomposition of Potassie Bromide, ete. 
by the action of cadmium or zinc upon water that has been 
thoroughly boiled, in a glass flask, provided with a long and 
very narrow outlet. Hven when no special pains are taken to 
preserve such water from contact with the atmosphere after 
the boiling, it is easy to perceive that peroxide of hydrogen 
does not readily form in it. So too, though in a lesser degree, 
with water that has been well nigh completely deprived of air 
by distillation in the vacuum of an air-pump. But no such in- 
ability to yield peroxide of hydrogen was observed in water 
that had been boiled for a long time in a copper flask, into the 
neck of which a long and very narrow brass tube had been so 
dered. The boiled water from the copper flask gave a reaction 
for the peroxide even when tested directly, without having been 
put in contact with any other metal. 
Iam much indebted to my assistant, Mr. D. S. Lewis, for his 
cooperation in this investigation. 
Bussey Institution, Jamaica Plain, Mass., June, 1876. 
Arr. XXIII.—Note on the double decomposition of Potassic Bro- 
mide and Sodic Chloride ; by J. H. Bru, Surgeon U. S. Army. 
In the practice of analytical chemistry it is the custom sf 
arranging and recording the results to associate the “ strong® 
acid” with the “ strongest base.” Thus, if barium, potassium, 
sulphuric and nitric anhydrides are found in a compound, 1 
the statement of the analysis we associate together the. ene: 
= sulphuric anhydride and the potassium and nitric anhy 
e. 
rates as an insoluble powder, the potassic nitrate remaining in 
solution a soluble crystalloid. ine, ale 
in, if potassium, sodium, chlorine and bro 
found in a mixture we record the results as so much Pia 
chloride and sodic bromide, or if we mix solutions of Y cal 
romide and sodic chloride we hold that potassic apie ble 
In this reeord nothing is assumed, for the basic sulphate sepa 
i¢ bromide exist in the mixture in consequence 0 55 oe 
decomposition. On what do we rest such an assalsp a 
it on anything more than analogy? The haloid salts 
sium and of sodium have nearly the same solubility, 
talline forms. We get no precipitate on mixing their soluon 
hor characteristic crystals on evaporating these, nor change - 
and crys 
