Nessler glasses

Equipment Nessler Cylinders (or Nessler Glasses) According to the British Standard Specification No 612, 966—a pair of cylinders made of the same glass and having the same diameter with a graduation mark at the same height from the base in both cylinders (Figure 1). 

Small quantities of phosphorus may be estimated quickly by the molybdate method, the amount of phosphomolybdate being estimated colorimetrieally by comparison in Nessler glasses or test-tubes with a standard prepared under conditions which are made identical as far as possible. An account of this estimation is given under Phosphoric Acid, p. 182. 

A similar method is used for the determination of inorganic phosphates in urine. 1 to 5 c.e. of the urine, containing about 0-5 milligram of phosphorus, are diluted and treated with a solution of ammonium molybdate in 15 per cent, sulphuric acid (5 c.c.), 1 c.c. of 1 per cent, hydroquinone solution and 1 c.c. of 20 per cent, sodium sulphite solution. The blue colour is compared in Nessler glasses with that developed by the same solutions when mixed with a standard phosphate solution of which 5 c.c. contain 0-5 milligram of phosphorus. 

Nessler tubes Cylinders of thin glass, generally graduated, used for comparing turbidities and colours of solutions. 

Standard Opalescence Place 1.0 ml of a 0.05845% w/v solution of NaCI in 10 ml of dilute HN03 in a Nessler cylinder. Dilute to 50 ml with DW and add 1 ml of AgN03 solution. Stir immediately with a glass rod and allow to stand for 5 minutes. 

Procedure Dissolve the specified quantity of the substance in DW, transfer to a Nessler cylinder, and the preparation of the solution. Dilute to 45 ml with DW, add 5 ml barium sulphate reagent, stir immediately with a glass rod, and allow to stand for 5 minutes. The turbidity is not greater than the standard turbidity, when viewed transversely. 

Simple colorimeters, used for routine analysis, are visual comparators related to Nessler tubes. The latter are made of flat-bottomed glass tubes with a volumetric mask and filled with reference solutions of varying concentrations (and possibly derivatising agents). The solution to be analysed, placed in an identical tube, is inserted beside the series of standard solutions. 

The spot-test technique is as follows. Mix a drop of the test solution with a drop of concentrated sodium hydroxide solution on a watch glass. Transfer a micro drop of the resulting solution or suspension to drop-reaction paper and add a drop of Nessler s reagent. A yellow or orange-red stain or ring is produced. 

A better procedure is to employ the technique described under the man-ganese(II) nitrate-silver nitrate reagent in reaction 9 below. A drop of Nessler s solution is placed on the glass knob of the apparatus. After the reaction is complete, the drop of the reagent is touched with a piece of drop-reaction or quantitative filter paper when a yellow colouration will be apparent. 

For general laboratory measurements water of specific conductance of about 1 X 10 ohm cm.- at 18° is satisfactory this can be obtained by distilling good distilled water, to which a small quantity of permanganate or Nessler s solution is added. A distilling flask of resistance glass is used and the vapor is condensed either in a block-tin condenser or in one of resistance glass. If corks are used they should be covered with tin foil to prevent direct contact with water or steam. 

Nessler tubes. Standardized glass tubes for filling with standard solution colors for visual color comparison with similar tubes filled with solution samples. 

Nessler s reagent. Dissolve 2.5 g of KI in 10 ml of water. Add saturated HgCl2 solution until a permanent precipitate forms. Add 25 ml of 30% NaOH solution, dilute to 200 ml with water, and mix well. Decant the clear solution from the precipitate, and store the solution in an amber-glass bottle. 

The simplest colorimeters, used for routine measurements, were visual comparators (Figure 9.31). Nessler tubes, used for many years, consisted of graduated flat-bottomed tubes of glass filled with different concentrations of standard solutions mixed with a derivatising agent. The solution to be analysed was placed with the same agent in an identical tube and colour was compared with that of the standards ( same colour, same concentration ). 

When 200 c.c. have distilled over, all the free ammonia has been removed, and it now remains to decompose the organie material, and determine the amount of ammonia formed. To-effect this, 50 c.c. of the permanganate solution a are added through the funnel to the contents of the retort, which is shaken, stoppered, and again heated. The distillate is now collected in separate portions of 50 c.c. each, in glass cylinders, until 3 such portions have been collected. These are then separately Ness-lerized as follows 2 c.c. of the Nessler reagent are added to the... 

To make the determination 100 c.o. of the water are placed in a glass cylinder and 1 c.c. each of solutions 1 and 2 added. Three other cylinders are at the same time prepare d, by diluting from 0.3 to 2.5 c.c. of solution 3 to 100 c.c. with pure H2O, and adding to each 1 c.c. each of solutions 1 and 2. The shade of color of the water-cylinder is then compared with that of the others, as described above in Nesslerizing. The amount of N2O3 in the water is equal to that in the comparison-cylinder having the same shade. 

Another and neater way of separating the crystals from the adherent mother liquor is to pack two balanced 12-ml centrifuge tubes each half full with glass wool, distribute the crystal mush equally between the two tubes so that they remain balanced, and centrifuge for a few minutes (see Chapter III). This salt is used in preparing Nessler s solution, a sensitive reagent for ammonia, and is worth keeping. It may, however, be used for the preparation to follow. 

Later in the nineteenth century the colour comparison in such procedures was made more accurate by placing the standard and unknown solutions in special tubes, known as Nessler tubes. These were made of glass with a flat base and were housed in a special rack which enabled them to be illuminated from below. The tubes were filled with an equal volume of standard or unknown solution and viewed from above. 

Color Comparison Tubes—Matched l(X)-mL, tail-form Nessler tubes, provided with ground-on, optically clear, glass caps. Tubes should be selected so that the height of the 100-mL graduation mark is 275 to 295 mm above the bottom of the tube. 

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