Tabulae atomicae : the chemical tables for the calculation of quantitative analyses of H. Rose : recalculated for the more recent determinations of atomic weights, and with other alterations and additions / by William P. Dexter.

  • Dexter, William P.
Date:
1850
Catalogue details

Licence: Public Domain Mark

Credit: Tabulae atomicae : the chemical tables for the calculation of quantitative analyses of H. Rose : recalculated for the more recent determinations of atomic weights, and with other alterations and additions / by William P. Dexter. Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    The last decimals, it will be seen, may be neglected without mate- rially affecting the result. The columns marked Logarithmus contain the logarithms of the numbers in the unit column of the same line.* For those who are familiar with their use, this will be found a very expeditious and con- venient way of making the calculation. It is, besides, free from all chance of error arising from a wrong placing of the decimal point; an error which, by the other method, may easily be committed. To perform the calculation by logarithms, we prefix to the loga- rithm given in the Table its proper characteristic, which is indi- cated by the adjoining number in the unit column, and add to it the logarithm of the number expressing the weight of the substance found. The result is the logarithm of the number required. To apply this to the above instance, we find in the Table the logarithm 8766580, and, as it is the logarithm of the decimal 0.75276, its characteristic is negative and unity. Adding to it the logarithm of 31.35, the weight of the chloride of silver found, viz. 1.4962375, we have 1.3728961 for the logarithm, and the number 23.599 for the weight, of the silver required. Calculations not expressly provided for in the tables may fre- quently be performed by a combination of two or more of the series * The column of logarithms is calculated directly from the atomic weights of the substances whose relation they express ; and, as they are carried to two more places of decimals, the results obtained in this way are more exact than those derived from a combination of the several numbers in the unit columns. In the instance cited in the text, the calculation, without the use of tables, would be performed, by the rule of three, as follows: — Ag CI: Ag: : 31.35 : x. By logarithms : — log. x = log. 31.35 -f [log. Ag — log. Ag CI]. Now the difference of the logarithms inclosed in the vinculum is a constant quantity for all values of the third term of the proportion; it is the logarithm given in the table, and is obviously that of the number in the unit column, supposing the decimal of the latter to be carried out to completion. 1 would add, that Rose considers logarithms as not leading to sufficiently accurate results tor the calculation of exact analyses. This is true if the logarithm be carried only to live decimal places; but if tables of seven decimals be made use of, the results will be found more exact than if made witli Rose's Tables.