On Tuesday, November 8, 2016 at 7:56:55 PM UTC-6, Sonny wrote:
Without analysing more (pics) of your chair, I suspect the armrests may have been cut off at the back, possibly after one broke. The backrest needs something for support.... I suspect, more so, than what your chair is showing.

Your chair may have had longer armrests, for supporting the backrest, as this chair:
http://antique-4-sale.com/images/mot...t---2380-3.jpg

Sonny

Or better yet, take a look at this Morris adjustable chair:
http://www.ebay.com/itm/Morris-Chair...-/252614907846

Google images for "Morris adjustable chair" and see if you can find one like yours.

https://en.wikipedia.org/wiki/Morris_chair

Sonny