"Horse chestnuts"are very bitter-they are not at all sweet like the European Chestnut. Can you remove the bitter acid from them? I recall reading that acorns can be made edible by crushing them and soaking in water-can you do the same with these chestnuts?
*Whew. *We used to call something quite different “horse chestnuts.” 
(Anyone else ever call them horse ockies?)
You mean, aside from Sherman T. Potter?
I call them conkers.
Horse pucky, 'round these here parts.
Horse chestnut (Aesculus spp.) seeds bear superficial resemblance to those of the unrelated chestnut (Castanea spp.) In California, native tribes mainly used to pound them into pulp and throw them into dammed streams to kill fish (well, stun them enough so they floated to the top to be grabbed). That’s how yummy they are.
We call them buckeyes here.
Sherman T. Potter said “Horse hockey”
Brits call them Conkers,
I’ve heard them called horse chestnuts or buckeyes in the states.
As to the OP, I have no idea. Except, i remember my grandmother had a tree in her backyard, and i loved throwing the spiked pods at my brother.
They can be. But they are much more toxic than acorns. It takes about a day to leach the tannins out of acorns to make them edible. Using the same process, buckeyes take more like ten days. The California tribes used them as a backup when the acorn crop failed.
Please, people - we are talking about two different species.
Aesculus hippocastanum is the horse chestnut; Aesculus glabra is the Ohio buckeye.
If you’re planning on storing up any available food to prevent starvation over the winter, I suppose it might be worth the effort to leach tannins out of these nuts.
Yes, and Aesculus californica is the CA buckeye.
However, most of the things in Ohio that get called buckeyes are actually horse chestnuts, and the true Ohio buckeye is mostly found in Kentucky. They’re named for the river, not for the state.
There are two Ohio buckeyes in my backyard.
Not much as ornamental trees - the flowers are white and unspectacular, and the leaves drop early without color (especially after dry summers).
It’s not just a matter of making it palatable, but of making it safe.
From NIH: http://www.nlm.nih.gov/medlineplus/druginfo/natural/1055.html
A nitpick I admit, but horsechestnut should be written as one word, or at least hyphenated, as it is not a chestnut: Just as russianolive, which is not an olive, baldcyprus which is not a cyprus, and redcedar which is not a cedar.
Should one also write, for instance, deadperson, because a dead person is not a person?
The heck? Who writes any of those as one word? This is a “rule” that does not exist in English.
Have never heard of a tree with that common name. Can you post the scientific name for that one? 
If you want to stick to and insist on using misnomer common names for trees, it’s none of my business.
Making them into one word or hyphenating them doesn’t make it any more “correct.”
And, yes, I’ll stick to the common names, of course. It’d look rather silly if I started writing out stuff as “jerusalemartichoke” or “mexicanoregano.”
I parse that as “Mexicano regano”. Nice rhythm to it. 