BAIRD &TATLOCK (LONDON) LTD. 



By means of the two axes of rotation, Q and s, the instrument is directed to the position which gives the clearest disc, with 

 the maximum of light. The screw G is rotated in order to make the zero of the vernier coincide with the zero of the scale. If 

 it is already regulated the two halves of the field will present a grey-yellowish shadow exactly equal in intensity. If it is not quite 

 regulated the appearance a or c will be observed. In order to bring about uniformity of shade it will be necessary to turn the 

 screw F, which is only employed for this purpose. This is turned in the right direction when the dark side becomes clear and 

 the clear side becomes dark. The position of uniformity of shade is reached when, in turning the screw c alternately to right or 

 left by fine movements, the appearance of b, Fig. 5897, to that of a or c, in order to stop finally at that of b, is successively observed. 

 When this is the case the appearance B should indicate zero on the scale. 



When the tube containing the sugar solution is interposed, the field must be focussed by drawing out o. The screw G is 

 then turned until uniformity of shade is established. 



Irregularity of shade at the neutral point is generally noticed. It arises when the flame is intense and the liquid under observa- 

 tion is very slightly coloured, and is due to the flame, which is not absolutely monochromatic. It is preferable in this case to 

 interpose the cap containing the bichromate crystal, which is placed in E. If there is not the same shade, grey-yellowish, an 

 exact point can be made by proceeding as follows : The line of separation in the centre of the two half-discs is fixed, and the 

 screw G turned alternately in one direction or the other until uniformity of shade is near. When the oscillations become slight 

 there is the appearance of a slight shadow which seems to go and to come from each side of this line, and the movement is arrested 

 when it seems stationary ; it now remains bright, and even disappears. At first no difference in colour is noticeable, but by 

 removing the eye for a moment, and again looking, a slight difference is observed. 



In the sugar industry it is often necessary to test juice and coloured syrups, and these, when placed in this apparatus (the 

 lever u being raised), or in any other saccharimeter, are frequently too dark coloured to be read. In such a case this apparatus 

 offers a resource that is possessed by no others, it permits of the lever u being lowered gradually, so that more light may pass into 

 the instrument. The advantage of being able to read with an approximation sufficient for ordinary work is thus possessed by the 

 instrument. In such cases it is impossible to see anything with other saccharimeters ; it avoids, more particularly, the decolourising 

 by animal charcoal, a long operation and liable to error by the quantity of sugar retained by the charcoal. 



It is advisable to determine the angle through which the lever is to be turned, since the angle obviously varies with the colora- 

 tion of the liquid. 



DESCRIPTION OF SMALL MODEL. 



The manipulation is the same as for the grand model, except that the levers j and K, which are vertical in the grand model, 

 are horizontal and to the right in the small one. The shaft x and the lever u do not exist, K is moved direct and J is fixed. In 

 the old models K carried some divisions which served as guide marks, but these are now dispensed with. 



The lamp is placed on the table at 20 centimetres from the polariser. 



CLEANING THE PRISMS AND LENSES. 



The apparatus is so constructed as to be separated into its different parts which can be carefully cleaned and freed from 

 dust or dirt. 



Polariser. B and I unscrew, the cap with bichromate crystal can then be taken out. The tube R is drawn out, the pin of 

 lever K is removed, freeing crank j. R being free, the interior cap containing a crystal of spar can be separated ; it also carries 

 a lens which unscrews. 



D is drawn out ; it is secured by a pin. 



Analyser. F unscrews, the tube H is drawn out, and the grooved tube removed, which contains a crystal of spar and a lens 

 which can be unscrewed. 



When cleaning the prisms and lenses, care must be taken not to scratch them. When H has been replaced, the screw F should 

 be secured and the zero re-established. The cap o being unscrewed, the small barrel carrying the concave eyepiece can be separated. 

 The lens N also unscrews. 



TUBES. 



It is now generally admitted that with this saccharimeter it is possible to read to -f^ of a division. It is necessary, in order 

 to profit by all the precision of the instrument, and to ensure the correctness of the result, that the accessories, such as the tubes, 

 graduated flasks, weights, etc., be equally correct. Each observation tube must be exactly the length it is stated to be. 



The makers attach a great importance to the construction of the tubes. For several years now the tubes have been made 

 with caps fitted with springs and bayonet joints, to replace the former very defective tubes, which had screw caps. They present 

 the following advantages : 



The length is calibrated, the ends are exactly plane parallel and at right angles to the axis of the tube. The end pieces are 

 of untempered plate glass with parallel faces. They are fixed by means of a spring confined in bayonet caps. The tubes are 

 accurately centred. 



In spite of the care in the execution, some of the readings may show a difference when the tubes are rotated in the instrument. 

 It is, however, possible to obtain correct readings as follows : A mark is made on the tube and it is rotated in several positions, 

 two or three times, for example, and the mean of the readings taken. A single reading will then be sufficient. 



ANALYSIS OF DIABETIC URINE. 



Use the divisions representing percentages of sugar. Take a flask graduated to 100-110 cubic centimetres, pour into it too 

 cubic centimetres of urine and add 10 cubic centimetres of basic acetate of lead. The uric acid as well as the colouring matter 



I is precipitated. Filter and fill up the 22 centimetres tube. If a tube of 20 centimetres was used, it would be necessary to add 

 to the result a tenth more. The rotatory power of the diabetic sugar (or glucose) is to that of cane sugar as 73 is to 100 ; that 

 is to say, 100 degrees of the saccharimeter corresponds to 22.2 grammes of diabetic sugar, dissolved in 100 cubic centimetres or 



I 222 grammes per litre, which makes 2.2 grammes per saccharimeter degree. In order to obtain the number of grammes of sugar 

 contained in a litre of diabetic urine it will be necessary then to multiply the number of degrees and tenths read on the sacchari- 



' meter by 2.22. 



Example. Urine read 5.2 sugar degrees, then 5.2x2.22 = 11 54 grammes glucose to a litre of urine. 



1077 



