Correction of the Standard of the Normal Solution of Sea Salt, when the Temperature changes

—We have supposed, in determining the standard of the normal solution of sea salt, that the temperature remained uniform. The a ays made in such circumstances, have no need of correction; but if the temperature should change, the same measure of the solution will not contain the same quantity of sea salt. Supposing that we have tested the solution of the salt at the temperature of 15° C.; if, at the time of making the experiment, the temperature is 18° C., for example, the solution will be too weak on account of its expansion, and the pipette will contain le of it by weight; if, on the contrary, the temperature has fallen to 12°, the solution will be thereby concentrated and will prove too strong. It is therefore proper to determine the correction nece ary to be made, for any variation of temperature. To ascertain this point, the temperature of the solution of sea salt was made succe ively to be 0°, 5°, 10°, 15°, 20°, 25°, and 30° C.; and three pipettes of the solution were weighed exactly at each of these temperatures. The third of these weighings gave the mean weight of a pipette . The corresponding weights of a pipette of the solution, were afterwards graphically interpolated from degree to degree. These weights form the second column of the following table, intitled, Table of Correction for the Variations in the Temperature of the Normal Solution of the Sea Salt . They enable us to correct any temperature between 0 and 30 degrees centigrade (32° and 86° Fahr.) when the solution of sea salt has been prepared in the same limits. Let us suppose, for example, that the solution has been made standard at 15°, and that at the time of using it, the temperature has become 18°. We see by the second column of the table, that the weight of a measure of the solution is 100·099 gr. at 15°, and 100·065 at 18°; the difference 0·034 gr., is the quantity of solution le which has been really taken; and of course we must add it to the normal measure, in order to make it equal to one you sand mill ièmes . If the temperature of the solution had fallen to 10 degrees, the difference of the weight of a measure from 10 to 15 degrees would be 0·019 gr. which we must on the contrary deduct from the measure, since it had been taken too large. These differences of weight of a measure of solution at 15°, from that of a measure at any other temperature, form the column 15° of the table, where they are expre ed in thousandths; they are inscribed on the same horizontal lines as the temperatures to which each of them relates with the sign + plus , when they must be added, and with the sign - minus , when they must be subtracted. The columns 5°, 10°, 20°, 25°, 35°, have been calculated in the same manner for the cases in which the normal solution may have been graduated to each of these temperatures. Thus, to calculate the column 10, the number 100·118 has been taken of the column of weights for a term of departure, and its difference from all the numbers of the same column has been sought. Table of Correction for the Variations in the Temperature of the Normal Solution of the Sea Salt. | Tem- per a- ture. | Weight. | 5° | 10° | 15° | 20° | 25° | 30° | | gram. | mill. | mill. | mill. | mill. | mill. | mill. | | 4 | 100,109 | 0·0 | - 0·1 | + 0·1 | + 0·7 | + 1·7 | + 2·7 | | 5 | 100,113 | 0·0 | - 0·1 | + 0·1 | + 0·7 | + 1·7 | + 2·8 | | 6 | 100,115 | 0·0 | 0·0 | + 0·2 | + 0·8 | + 1·7 | + 2·8 | | 7 | 110,118 | + 0·1 | 0·0 | + 0·2 | + 0·8 | + 1·7 | + 2·8 | | 8 | 100,120 | + 0·1 | 0·0 | + 0·2 | + 0·8 | + 1·8 | + 2·8 | | 9 | 100,120 | + 0·1 | 0·0 | + 0·2 | + 0·8 | + 1·8 | + 2·8 | | 10 | 100,118 | + 0·1 | 0·0 | + 0·2 | + 0·8 | + 1·7 | + 2·8 | | 11 | 100,116 | 0·0 | 0·0 | + 0·2 | + 0·8 | + 1·7 | + 2·8 | | 12 | 100,114 | 0·0 | 0·0 | + 0·2 | + 0·8 | + 1·7 | + 2·8 | | 13 | 100,110 | 0·0 | - 0·1 | + 0·1 | + 0·7 | + 1·7 | + 2·7 | | 14 | 100,106 | - 0·1 | - 0·1 | + 0·1 | + 0·7 | + 1·6 | + 2·7 | | 15 | 100,099 | - 0·1 | - 0·2 | - 0·0 | + 0·6 | + 1·6 | + 2·6 | | 16 | 100,090 | - 0·2 | - 0·3 | - 0·1 | + 0·5 | + 1·5 | + 2·5 | | 17 | 100,078 | - 0·4 | - 0·4 | - 0·2 | + 0·4 | + 1·3 | + 2·4 | | 18 | 100,065 | - 0·5 | - 0·5 | - 0·3 | + 0·3 | + 1·2 | + 2·3 | | 19 | 100,053 | - 0·6 | - 0·7 | - 0·5 | + 0·1 | + 1·1 | + 2·2 | | 20 | 100,039 | - 0·7 | - 0·8 | - 0·6 | 0·0 | + 1·0 | + 2·0 | | 21 | 100,021 | - 0·9 | - 1·0 | - 0·8 | - 0·2 | + 0·8 | + 1·9 | | 22 | 100,001 | - 1·1 | - 1·2 | - 1·0 | - 0·4 | + 0·6 | + 1·7 | | 23 | 99,983 | - 1·3 | - 1·4 | - 1·2 | - 0·6 | + 0·4 | + 1·5 | | 24 | 99,964 | - 1·5 | - 1·5 | - 1·4 | - 0·8 | + 0·2 | + 1·3 | | 25 | 99,944 | - 1·7 | - 1·7 | - 1·6 | - 1·0 | 0·0 | + 1·1 | | 26 | 99,924 | - 1·9 | - 1·9 | - 1·8 | - 1·2 | - 0·2 | + 0·9 | | 27 | 99,902 | - 2·1 | - 2·2 | - 2·0 | - 1·4 | - 0·4 | + 0·7 | | 28 | 99,879 | - 2·3 | - 2·4 | - 2·2 | - 1·6 | - 0·7 | + 0·4 | | 29 | 99,858 | - 2·6 | - 2·6 | - 2·4 | - 1·8 | - 0·9 | + 0·2 | | 30 | 99,836 | - 2·8 | - 2·8 | - 2·6 | - 2·0 | - 1·1 | 0·0 | Several expedients have been employed to facilitate and abridge the manipulations. In the first place, the phials for testing or a aying the specimens of silver should all be of the same height and of the same diameter. They should be numbered at their top, as well as on their stoppers, in the order 1, 2, 3, . They may be ranged succe ively in tens; the stoppers of the same series being placed on a support in their proper order. Each two phials should, in their turn, be placed in a japanned tin case ( fig. 90. ) with ten compartments duly numbered. These compartments are cut out anteriorly to about half their height, to allow the bottoms of the bottles to be seen. When each phial has received its portion of alloy, through a wide-beaked funnel, there must be poured into it about 10 grammes of nitric acid, of specific gravity 1·28, with a pipette , containing that quantity; it is then exposed to the heat of a water bath, in order to facilitate the solution of the alloy. The water bath is an oblong ve el made of tin plate, intended to receive the phials. It has a moveable double bottom, pierced with small holes, for the purpose of preventing the phials being broken, as it insulates them from the bottom to which the heat is applied. The solution is rapid; and, since it emits nitrous vapours in abundance, it ought to be carried on under a chimney. IMG:4147767755307473660_illo0073.png:Phial rack and agitator