Lessons in elementary chemistry : inorganic and organic / by Henry E. Roscoe.

Date:
1869
Catalogue details

Licence: Public Domain Mark

Credit: Lessons in elementary chemistry : inorganic and organic / by Henry E. Roscoe. Source: Wellcome Collection.

Provider: This material has been provided by the Royal College of Physicians of Edinburgh. The original may be consulted at the Royal College of Physicians of Edinburgh.

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    III.] and those below the freezing point are characterised by a minus sign, thus, —1° C, —20 C, &c. Fahrenheit divided the same space into 180 equal parts, each of which is called a degree Fahrenheit; he did not, however, com- mence his scale at the freezing point, as he erroneously thought that he had obtained the greatest possible degree of cold by making a mixture of snow and salt ; the tem- perature of this mixture he found to be 32 of his degrees below the freezing point of water ; he, therefore, called the freezing point 32°. In Fahrenheit's scale, minus numbers are employed to denote degrees of temperature below the Zero of his scale ; this scale is the one in com- mon use in England, but is the most inconvenient one which we could adopt. Reaumur's scale (used in Russia and Sweden) resembles the Centi- f c r grade scale, except that the space between the freezing and boiling points is divided into 80 equal parts ; so that water boils at 80' Reaumur. The connexion be- tween these three scales is seen at a glance by reference to Fig. 8. The relation between the de- grees Fahrenheit, Centigrade, and Reaumur is expressed by the numbers 9, 5, 4. In converting from degrees Fahrenheit to Cen- tigrade or Reaumur, we must re- member first to subtract 32 and then reduce ; whilst when pass- ing from degrees Centigrade and Rdaumur to Fahrenheit we must add 32 after the multiplication Fls- 8- and division are completed. I f very exact measurements are required, several precau- tions must be taken in the graduation and use of thermo- meters : thus, for instance, the tube must be calibrated— that is, the irregularities in the bore must be determined 212 juo 80