212 ANNUAL OF SCIENTIFIC DISCOVERY. 



acid alone. 2d. The solution of iodide of potassium must not be 

 added, to the mixture of sulphuric acid and liquid till cold, or iodine is 

 apt to be liberated without the presence of nitric acid. 3d. The pro- 

 portion of sulphuric acid added to the suspected liquid must not be 

 too great, or the most dilute solution of iodide of potassium gives 

 iodine without nitric acid. 4th. As a solution of hydriodic acid, formed 

 by the action of sulphuric acid upon iodide of potassium, is decomposed 

 by the air in the course of an hour or two, and a blue formed with starch, 

 unless a distinct color is produced in ten or fifteen minutes, it may be 

 concluded that nitric acid is not present. I dissolve 25 grs. of iodide 

 of potassium in 16 oz. of water for the test solution, which is too dilute 

 to give iodine with sulphuric acid alone. To the suspected liquid, in a 

 test tube, I add not more than one sixth of its bulk of concentrated 

 sulphuric acid ; heat nearly to boiling, and keep hot in the sand-bath 

 for several minutes ; cool the tube in cold water, and add a drop of 

 starch-mucilage and a few drops of the test solution. If nitric acid is 

 present, the liquid assumes a blue, very intense, with even one five- 

 hundredth part of nitric acid. With one five-hundredth part by 

 weight of NO 5 , intense dark blue ; one one-thousandth part of do. do., 

 dark blue ; with one five-thousandth part, do. do., dark blue ; with one 

 ten-thousandth part, do. do., paler blue ; with one twelve-thousandth 

 part, do. do., pale blue ; with one sixteen-thousandth part, do. do., blue 

 tint ; with one eighteen-thousandth part, do. do., blue tinge ; with one 

 twenty-thousandth part, do. do., faint blue tinge, becoming decided in 

 a few minutes. 



It is remarkable that, even with the great excess of sulphuric acid 

 present, the whole of the nitric acid is not liberated until after heating 

 some time ; thus, one sixteen- thousandth part required ten minutes 

 heating before the test could indicate nitric acid ; one eighteen-thou- 

 sandth part I heated twenty minutes ; and one twenty-thousandth part I 

 found necessary to heat half an hour before testing. Probably, by ob- 

 serving the same method, the other tests for nitric acid, viz., proto- 

 sulphate of iron, sulphate of indigo and gold-leaf, might become more 

 delicate ; but this I have not tried. Of course, some other acids would 

 give the same results, as the chloric and chromic acids, &c. ; but the 

 absence of these is easily ascertained, and they seldom occur in anal- 

 ysis. 



NEW TEST FOR THE NITRATES AND NITRITES. 



AT the American Association, New Haven, Mr. G. C. Schcefier fur- 

 nished the following new test for the nitrates and nitrites : To the 

 solution supposed to contain a nitrite, add one or two drops of solution 

 of yellow prussiate of potash ; there should not be enough to give a 

 perceptible tinge to the liquid. A few drops of acetic acid are then to 

 be added, and immediately, or in a few minutes, according to the 

 quantity of nitrite present, the liquid assumes a rich yellow tint ; as 

 the reagents used give nearly the same color spontaneously after some 

 time even in pure water, it is better, when testing for minute quanti- 

 ties, to use two similar vessels, one containing pure water and the 

 other the liquid under examination, to both of which the reagents are 

 to be added in precisely equal quantities. The vessels should be equally 



