A manual of practical chemistry for public health students : especially arranged for those studying for the D.P.H / by A.W. Stewart.

  • Alfred Walter Stewart
Date:
1913
Catalogue details

Licence: In copyright

Credit: A manual of practical chemistry for public health students : especially arranged for those studying for the D.P.H / by A.W. Stewart. Source: Wellcome Collection.

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    of solution and ’0053 x 14 X 10= amount of Na2C03 in 100 c.c. of solution, whence 100 grm. soda ash contains ■9953 X 14 X 10 x 100 = 74-2 per cent. N2C03. Preparation of Decinormal Permanganate of Potash, tn<t KMnO Here we require to find out how much permanganate corresponds to the equivalent weight of oxygen (= 8), which is the active principle in the substance. This is got from the following equation :— 2KMn04 + 3H2S04=50 + 3H20 + K2S04 + 2MnS04 i.e.,2 x 158 = 5 x 10 (oxygen) 3i6 =80 3i-6 =8 — equivalent weight of oxygen = N. solution 3‘i6= '8 = solution Weigh out accurately 3-16 grm. of KMn04, dissolve in water and make up to 1,000 c.c. in a graduated flask. Estimation of Ferrous Iron in Ferrous Sulphate (Sulphate of Iron). This is effected by means of the permanganate solution. Weigh out 5 grm. sulphate of iron ; dissolve in water and make up to 250 c.c. in a graduated flask. Pipette 25 c.c. into a flask, add 20 c.c. H2S04 (1 in 4) and then run in j~j KMn04 until a permanent pink colour is obtained. The oxygen from the KMn04 oxidizes the ferrous salt to the ferric state. The following is the equation :— [Ferrous sulphate] [Ferric sulphate] 10FeS04 4- 2 KMn04 + 8 HaS04 =5 FeJSCU, + 2 MnS04 + 8H20 + K2S04 “ The oxygen is more in evidence in the following equation :— [Ferrous ox hie] [Ferric oxide] 2 FeO + O = Fe203 112 16 From this we see that 2 x 56 = 112 Fe correspond to 16 oxygen. 56 Fe correspond to 8 oxygen (equivalent weight). Hence an TN„ Fe = 5-6 grm. per litre, i.e., 1 c.c. = -0036 grm. Fe.