THE CHEMISTRY OF THE ANIMAL BODY. 505 



heat, the latent heat of steam. For 1 gram of water this absorption amounts to 536.5 

 calories. This property of water is of great value to life, for through the heat absorbed in 

 the evaporation of sweat the temperature of the body is in part regulated. 



Peroxide of Hydrogen, H 2 2 , is found in very small quantities in the air, 

 in rain, snow, and sleet, and where there is oxidation of organic matter. 

 Preparation. — (1) By the action of sulphuric acid on peroxide of barium, 

 Ba0 2 + H 2 S0 4 = BaS0 4 + H,< >,. 



(2) Peroxide of hydrogen is a product of the oxidation of phosphorus, and generally 

 exists wherever ozone is produced. 



(3) Peroxide of hydrogen exists wherever nascent hydrogen acts on oxygen. 

 It is therefore found mixed with hydrogen evolved at the negative pole in the 

 electrolysis of water. This action happens in putrefaction, where the nascent 

 hydrogen unites with any oxygen present, and the resulting H 2 2 strongly 

 oxidizes the organic matter through the free — O — atom liberated. 1 



Properties. — Peroxide of hydrogen is a colorless, odorless, bitter-tasting 

 fluid, which decomposes slowly at 20° F., and with great violence at higher 

 temperatures. It oxidizes where ordinary oxygen is ineffective ; it is a powerful 

 bleaching agent, and is used to produce blonde hair. It destroys bacteria. Blood- 

 corpuscles brought into a solution of H 2 2 bring about its rapid decomposition 

 into water and atomic oxygen, whereby oxygen is evolved and oxyhemoglobin 

 is converted into methsemoglobin. If oxyhemoglobin be brought into a 

 putrefying fluid, the nascent hydrogen withdraws oxygen from combination 

 to form H 2 2 , and then the atomic oxygen reacts on haemoglobin to form 

 methaemoglobin. 2 The formula for the peroxide is probably II — O — O — H. 

 In certain cases peroxide of hydrogen has a reducing action. 



Theory of Hoppe-Seyler 3 to account for the Oxidation in the Body. — This 

 maintains that, as in putrefaction, hydrogen is produced in the decomposition 

 of the cell, and acting on the oxygen present converts it into peroxide with 

 its unstable atom, which then splits off as active oxygen and effects the oxida- 

 tion of the substances in the cell. This theory is easier to reconcile with the 

 fact that oxidation is dependent on the amount of decomposition (see p. 501) 

 than is the theory of Traube. 



Solutions of H 2 2 do not liberate iodine from potassium iodide immediately, but only 

 on the addition of blood-corpuscles or of ferrous sulphate, which cause liberation of — — , 

 and then any starch present may be colored blue (see p. 502). Gruaiacum is not affected 

 by H,0 2 unless blood-corpuscles or ferrous sulphate be added to make the oxygen active. 



Sulphur, S = 32. 



Sulphur is built in the proteid molecule of the plant from the sulphates 

 taken from the ground. It is found in albuminoids, especially in keratin. As 

 taurin it occurs in muscle and in bile, as iron and alkaline sulphide in the 



1 Hoppe-Seyler: Zeitschrift fur physwlogische Chemie, 1878, Bd. '_\ 8. 22. 



2 Hoppe-Seyler, Op. cit., S. 26. 



3 P0ijir.< ArchiVf Bd. L2, S. 16, 1876. See also Berichte der deutschen ehemischen QaeUaehqfl, 

 Bd. 22, S. 2215. 



