Taking the generally-accepted specific gravity of water at its greatest density—i.e. at 4° as one—it has been shown by experiment that the specific gravity of water at different temperatures is as follows: At 0° 0·99987 At 30° 0·99574 „ +10° 0·99974 „ 40° 0·99233 „ 15° 0·99915 „ 50° 0·98817 „ 20° 0·99827 „ 100° 0·95859 A comparison of all the data at present known shows that the variation of the specific gravity S_t with the temperature t (determined by the mercurial thermometer) maybe expressed (Mendeléeff 1891) by the formula S_t = 1 - (t - 4)² / (94·1 + t) (703·51 - t) 1·9 t° C. according to the mercurial thermometer Sp. gr. S_t (at 4° = 1,000,000) Variation of sp. gr. with a rise of Volume taking vol. at 4° = 1 Temp. per 1° C. or ds/dt Pressure per 1 atmosphere or ds/dp -10 998,281 +264 +54 1,001,722 0 999,873 +65 +50 1,000,127 10 999,738 -85 +47 1,000,262 20 998,272 -203 +45 1,001,731 30 995,743 -299 +43 1,004,276 50 988,174 -450 +40 1,011,967 70 977,948 -569 +39 1,022,549 90 965,537 -670 +41 1,035,692 100 958,595 -718 +42 1,043,194 120 943,814 -819 +43 1,060,093 160 907,263 -995 +55 1,102,216 200 863,473 -1,200 +73 1,158,114 If the temperature be determined by the hydrogen thermometer, whose indications between 0° and 100° are slightly lower than the mercurial (for example, about 0·1° C.