EEPOBT OF CHEMICAL LABORATORY 



243 



presence of the meniscus just mentioned introduces a difficulty. In order to obviate this, the 

 arrangement showTi in Fig. 102 has been devised, and has been found to answer the purpose 

 admirably. It consists of an ordinary form of hydrometer provided vdth a float which is 

 used in the graduation of the instrument. The reading is made, not at the surface of the 

 liquid, but at the point where the top of this float cuts the stem of the hydrometer. See 

 Figs. 103 and 104. 



The float consists of a hollow ring of glass supporting an upright short section of amber- 

 coloured glass tubing, cut oft' at a slight angle, the uppermost portion of the tube being used 

 as the index. (An alternative arrangement is a short section of colourless glass tubing with 

 a straight line etched on its surface.) In this way, error arising from the presence of the 

 meniscus is avoided, and fractional parts of a degree may be read with the greatest ease. 



The float has a fragile appearance, but the one made for us by C. Kob and Co. has been 

 in use over a year and remains unbroken. It could doubtless be made of thin metal, gold 

 plated, if desired. 



When only small quantities of li(piiil are available the form of jar shown in Fig. 102 may 

 be adopted with advantage. The upper portion is flared in order to receive the float but the 

 lower portion of the jar is only slightly larger than the bulb of the hydrometer. 



In use it is essential that the stem remain dry in order that it may not stick to the 

 upright tube of the float. Wetting of the stem may be avoided by proceeding as follows : — 

 The stem of the hydrometer being dry the float is passed over it and allowed to rest on the 

 bulb. The hyilrometer is then lifted by the point of the stem and gradually let into the 



liquid. If there is any doubt as to the instru- 

 ment having found its proper level, the base 

 of the hydrometer jar may be held firmly to 

 the table by one hand and the jar gently tapped 

 with the other. 



When removing the hydrometer the float 

 should be taken out first, in order to keep the 

 tube dry and ready for a second test if required. 



Determination of " Crude Fibre." 



Fig. IO.S.— a Simple Arrangement for Determination 

 OF " Crude Fibre" 



The method of determining crude fibre 

 most generally in use consists in boiling the 

 fat-freed material fur half an hour with 1'25 

 per cent, sulphuric acid and 1-25 per cent, 

 sodium hydroxide solution successively. The 

 boiling is effected in a flask provided with an 

 inverted condenser, in order to avoid concen- 

 tration of the liquid. The method is usually 

 very troublesome, as the Liquid foams and the 

 solid is carried up into the condenser tube from 

 which it is dislodged only with difficulty. 



The simple arrangement exhibited in 

 Fig. 105 is free from the above defect, and the 

 manipulation generally is much easier. The 



Determina- 

 tion of 

 Crude Fibre 



