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Blackboard Frames. Darkening Apparatus. 



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moved witli ease in an up and down direction, and has thin red vertical and horizontal lines every . s. d. 

 10 cm. which are easily visible. Hit only a short distance away. 



The stink cupboard is 1.50 m long, 70 cm deep and about 2.30 m high. It is constructed of ; 

 pitch pine. The upper part is glazed and lias a sliding window in front suspended on gill strings, being | 

 maintained in any desired position by counterpoises. The top (which is sloping) is glazed. The water 

 resulting from precipitation is collected in a lead gutter arranged in front, and this water is conducted 

 to a lead vessel placed laterally. The table top is a polished slate slab mounted in oak frame. The 

 substructure is built as a cupboard for taking a battery of accumulators. The cupboard is in commu- 

 nication with the draught pipe proper by holes drilled in the table top: thus the gases which are 

 generated while the accumulator is charging escape through the draught pipe. In order to accelerate 

 the dissipation of the poisonous gases and to prevent their entry into the s-hool room, an electrically- 

 driven ventilator is fitted in the wall at the back of the upper part of the cupboard. By means of 

 a hand wheel the accumulators can be switched on from the outside for the various purposes for which 

 they are intended to be used. The stink cupboard has water inlet and waste, the cock being placed under 

 the table on the outside. The outlet orifice is placed inside the cupboard at the back, above a lead 



basin let into the slate slab. A gas supply lead with two supply points has likewise 2 taps outside; 

 the orifices, in the form of hose unions, being inside the cupboard. A third tap is intended for the 

 draught flame. The various leads are laid on complete to the floor. The back is open, and the cup- 

 board should be placed close up against the wall, and before erecting the cupboard, the wall must be 



plastered with cement or laid with tiles. 



50.176. Blackboard T-square, with centimetre graduations, 1 m long (W. D., Fig. 48 [Fig. 44]) 0. 3. 



50.177. Blackboard Triangular Set Square, graduated 0. 3. 6 



50.178. Blackboard-Triangle . 0. 4. 



50,17<>. Blackboard Ruler 0. 1. 6 



50.180. Wood Compasses with brass bow 0. 8. 



50.181. Wall Stink Cupboard (or hood for escaping gases), Figure on p. 27, 1.2 m long, 

 o.'t m high, 0.6 m deep, lined with 4 polished slate slabs, with holes for the gas used 



for heating and lighting, and with opening to the draught flue (see also Plate II, p. 5) ; 12. 0. 



The wall stink cupboard has both on the class room and preparation room sides a sliding window 

 of the size of the portion of wall cut away, to allow of the cupboard being opened and closed. In the 

 preparation room the cupboard has a table substructure with oak top, while in the Class Room the 

 substructure of the blackboard fulfils the object of table. 



If desired, the cupboard can be done out with glazed slabs, in which case we supply a porce- 

 lain shutter for building into the wall, for shutting off the lower orifice of the draught flue. For the pur- 

 pose of obtaining good ventilation, it is advisable to have square acid-proof clay pipes for building or 

 fixing into the wall, with additional pieces for closing at the roof. 



On erecting the building, a suitable opening should be provided in the wall. 



Darkening Apparatus. 



General Remarks, The devices consist of roller blinds of black, light-tight felt fixed to shafts composed 

 of Mannesmann tubes. The rods rest in iron wall bearings placed above the windows. At the lower 

 end the blinds have weighting bars and move over guide bars and between broad wood frames of CZ 

 shaped section. These frames are so constructed that they completely surround the windows. 

 When a number of windows in a row or on more than one side of a room are to be darkened 

 simultaneously, the iron rods are coupled together or connected above the corners of the room 

 by couplers. For facilitating transport the frames are delivered in single sections which have 

 to be assembled on receipt. 



The substantial construction of the bearings and the power- 

 ful transmission shafts, which can be made to any size, are an absolute 

 n e c c s s i t y. The question of cheapness should not be allowed to decide, but if the devices 

 are to work continuously with certainty, the main question is construction as regards 

 the woodwork of the frames, the material and the transmission parts. 



The material of which the curtains are made is of primary importance. This is manufactured 

 expressly for the purpose; it is absolutely light-tight and moth-proof, and consists of 3 layers 

 bound together - - a product of many years' experience. The fabric is .3 5 mm thick. This 

 thickness is necessary to obviate any chance of the curtains shrinking and to offer sufficient resis- 

 tance to the draught. The disadvantages of darkening the windows by roller blinds can always 



Stink Cupboards see pages 48 to 52. 



