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Hardwood Record — Veneer & Panel Section 



July 10, 1918 



stem. When ordering hydrometers the Hquid for which 

 the instrument is intended must be specified. Combined 

 mstruments usually cost about 60 to 1 00 per cent more 

 than plain. 



In operating the hydrometer, pour a sample of the 

 glue solution to be tested into the vessel and let the in- 

 strument slowly sink into the solution until it finds its 

 correct position. If the solution is made up of two parts 

 water and one part glue, the hydrometer will drop to 

 33 1 3 on the scale, which will show that there is 33 1 3 

 per cent dry glue in the solution. The operator must 

 always keep in mind what corrections are necessary on 

 account of the difference between the temperature of the 

 solution and the arranged temperature of the hydrometer. 



The particular advantage of the hydrometer is that 



no special skill is required to use it, and readings may 

 be quickly made. It may be immersed in any of the glue 

 solutions about the plant, for the purpose of determin- 

 ing whether or not the solution is at the regular factory 

 standard. 



The viscosity, or fluidity, test is based on the idea that 

 the greater the tenacity of the glue, the greater will be 

 its cohesiveness, and the less will be its flowing power. 

 In viscosity testa water is used as a standard, and the 



rate of flow of a solution, at a certain temperature, is 

 compared with the rate of flow of water under the same 

 conditions. In accurate viscosity tests it is advisable to 

 weigh carefully all test portions, and to time the flow 



of the glue liquid on a stop watch showing as fine as fifths 

 of seconds. In factory practice, however, it is customary 

 to use an ordinary watch. 



Several devices are on the market under the name of 

 viscometer, or viscosimeter, for measuring the viscosity 

 of the glue solution. While they vary in detail they are 

 in principle a burette, or pipette, through which the glue 

 is allowed to flow^ at a given temperature. A burette 

 (figure IV) is a fine graduated glass tube, open at one 

 end, and narrowed at the other to an almost capillary 

 tube. Near the narrowed end is a tap for regulating the 

 flow of the liquid. A pipette (figure V) is usually smaller 

 than a burette, in all proportions, and has no tap. Flow 

 from a pipette may be regulated by pressure of a finger 

 on the top opening of the tube. The pipette usually is 

 not graduated, but has a "standard" mark. While 

 laboratory tests are made with solutions containing as 

 small as one per cent of dry glue, it is most common fac- 

 toiy practice to use 20, 25 or 33 1 3 per cent solutions. 

 The manner of procedure may be varied to suit indi- 

 vidual desires. TTie initiatory action consists in accurately 

 weighing one part dry glue and two parts water in reason- 

 ably small proportions. The water should be cool. Be- 

 tween 50 and 65 degrees F. is a good temperature. Let 

 the glue soak in the water about 1 2 hours. For soaking 

 purposes it is well to have a vessel about two inches in 

 diameter and four inches deep, fitted with a detachable 

 cover. As an auxiliary to this vessel have another about 

 three inches in diameter and five inches deep, fitted with 

 a perforated false bottom about an inch from the solid 

 bottom. After the glue has soaked the required time, 

 fill the auxiliary vessel approximately half full of hot 

 water. Heat, in any convenient way, until the water 

 reaches about 200 degrees F. Then put the vessel con- 

 taining the glue solution into the water. (See figure VI.) 

 Keep the heat on until the glue is thoroughly dissolved. 

 Then the water should be about 2 1 2 and the glue about 

 190 degrees F. TTien open the vessel containing the glue 

 and stir the mixture until certain there is nothing left 

 undissolved. Lift out the vessel and take the tempera- 



