BAIRD &TATLOCK (LONDON) LTD. 





4860 



4861-4862 



Specific Gravity of Gases. 



We draw attention to two new instruments recently invented by Simmance & Abady for automatically and 

 ontinuously indicating and recording the specific gravity of gases both lighter and heavier than air. 



The principle employed and patented by Messrs. Simmance & Abady appears from the Patent Office records 

 D be quite original. It consists simply of passing the gas continuously over the crown of a suspended bell and 

 hence up a vertical tube. If air is so passed, the weight of the ascending stream above the crown of the bell 

 ; equal to the weight of the air ( = i) beneath it and the pointer remains at zero. If the gas is lighter than air 

 hen the weight of the ascending stream above the crown of the bell is lighter than the weight of the air beneath 

 : and the bell naturally rises in exact proportion to the gravity while the pointer of course moves over the scale 

 nd stops when equilibrium is reached and thus indicates the specific gravity on the lower scale which is figured 

 om i (zero) to o. If it is desired to indicate the gravity of a gas heavier than air, then by counter-balancing 

 :ie bell with a weight equal to the weight of the column of air equilibrium is obtained at the other extremity 

 f the scale and if a heavy gas is passed through the instrument the bell will fall and the pointer moves over 

 he scale and so indicate the gravity of gases heavier than air on the upper scale which is figured from I (zero) to 2. 



The instrument works absolutely automatically and indicates changes of gravity instantaneously and can 

 c easily read to the third place of decimals. It has practically no moving parts and its accuracy has been 

 cmonstrated by series of experiments extending over many months. 



It will probably occur to those who have worked with gases that the gravity of a given volume of gas will 

 ary with changes in temperature and atmospheric pressure. In the Simmance-Abady Gravitometer, however, 

 : will be seen that the automatic weighing always takes place in comparison with air under similar conditions 

 f temperature, etc., to those of the gas, and that therefore it is the true specific gravity which is always indicated, 

 "ithout the necessity of any correction. 



860 T Simmance & Abady's Patent Gravitometer, with two scales for automatically and 

 continuously indicating the specific gravity and changes in composition of gases both 

 lighter and heavier than air .. .. .. .. .. .. .. 1210 



861 1 Simmance & Abady's Patent Gravitometer, with pen for automatically and con- 

 tinuously recording on a chart the specific gravity and changes in composition of gases 

 lighter than air, with 100 charts . . . . . . . . 14 10 



862 T Simmance & Abady's Patent Gravitometer, No. 4761, with pen for automatically and 

 continuously recording on a chart the specific gravity and changes in composition of 

 gases heavier than air, with 100 charts . . . . . . 14 10 



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