From Patent #180842, filed August 1876 by W.H. Burt.
“My invention is designed to produce a pocket spirometer, by which the breathing-capacity of a persons lungs can readily be measured in cubic inches, by mercury, oil, glycerine, spirits, water, or all other liquid substances. It consists of a simple glass tube with a small bulb at the base lilled with mercury or other liquid, upon which bulb is a rubber tube with a mouth-piece; also, a vertical scaled tube, into which the mercury or other liquid is blown for testing the lungs in cubic inches.
“The drawing is partly a side elevation and partly a sectional elevation of my improved spirometer.
“A is the glass bulb, for containing the mercury or other liquid substance. B is the rubber tube, with a mouth-piece, O, and D is the scaled tube for measuring the height of the column raised by the lungs. The rubber tube connects with a nozzle on the top of the bulb, and the glass tube connects with the bottom of the bulb by a return bend. The top of the vertical tube is open to the atmosphere, to prevent compressing the air above the liquid, and a little cap, E, may be used for closing it, to exclude dust, &c., and preventing the liquid from running out by pneumatic pressure. This cap must be taken off when in use. Or, the top of the scaled tube and mouth-piece may have a funnel-shaped glass blown into the top of each, which will prevent the liquid from running out, and the cap can be dispensed with; or a cork may be put into the nozzle, and also in the tube, to retain the liquid, in which case both the cap and funnel-shaped glass will not be required. When in use, this cork must be removed, or the instrument will not work.”
This spirometer appears to have been manufactured and sold because it was reviewed by Eldridge C. Price, MD in the 1884 issue of Medical Times (Volume 12, page 40):
“Burt’s instrument requires a maximum amount of muscular strength, and in the haemmhorragic diathesis its use is dangerous. In fact the instrument is nothing but a modified manometer, and is no index of lung capacity. I have seen the worthlessness of this instrument as a spirometer illustrated, when a well-muscled man of 5 feet 7 inches of height, who at one sudden and powerful expiration forced the mercury above the 300 cubic inch index, a few grains even shooting out of the tube. This gentleman’s actual respiratory capacity by future accurate mensuration proved to be 248 cubic inches.”