how do i win with alch? 4 losses in a row, literally challenge.
Farm fast and get some good items then man mode in team fights. The draw to Alchemist is that he can farm, and he can farm faster than anyone else. Outside of that fact he's a rather underwhelming carry. Yes, he has a great stun and decent minus armor from Acid Spray but compared to say a built in crit, bash, escape, or evasion he is lacking compared to hard carries like Void, AM, and PA. His biggest feature is that he can get six slotted by the 30 minute mark if you're a god amongst men. He also has a lot of optons but needs a lot of consideration when it comes to his farm;
Can you get a Midas in under 7 minutes? Then do it and go from Midas to Treads\Phase (really a matter of opinion) to a Maelstrom and then pick up a BKB. If you're farming correctly you should be able to get that by the 20-25 minute range (if I remember correctly), once you get that BKB co-ordinate with your team and force team fights. Pop ulti and bkb and stun someone and beat the crap oughta them. Finish your Mjollnir, and transition to something that helps you beat their biggest threat. Void or PA on their team? Get an MKB. Lots of right click threats? Consider an HH for disable and evasion. Worried about dying before you can dish out damage? Get a Heart. Against a carry like Lifestealer or AM that can escape with ease? Basher is your bff.
Can't get a 7-8 minute midas? Ignore it. Greevil's Greed is enough to give you above average farm as is. Consider going for an early Basiliius + Treads then getting a Vlad's and Maelstrom. This will give you enough sustainability with your ulti to effectively never need to go back to fountain, and then get your BKB. If all goes according to plan should be about the 25-30 minute range (if I remember correctly). See above after that.
I personally almost always get Vlad's on Alchemist. It's a damn good item if you can get it early and in my mind gives everything Alchemist needs in the early game--Lifesteal, Mana, Damage. It's not a ton of any single category but it's an item you can use as a placeholder while farming your big ticket items. I cannot recommend it enough.
As for how to actually play, you can either play a 1 slot or 3-4 slot Alch. I've assumed you were going for the prior so I'll address that. Get the safelane, and try and figure out who you'll be against before leaving the fountain. Up against someone with a lot of right click, grab a stout shield, it wll help you quite a bit and it's not a huge loss. I also always recommend a quelling blade for last hitting since it's a small price to pay for 30% more damage to creeps. You're gonna want to stay in lane and keep the lane pulled back as much as you can, which means getting support to stack and pull and/or hoping you're laning against someone like Kunkka, DS, or DP who always push the lane. If you can get a support to babysit you, especially one with a disable, you can easily pull a first blood by starting your stun then having them jump the person--saving your disable until they are potentially getting away (popped Windrun or Surge) or to maximize the stun time/damage. I've also seen some people go Soul Ring + Tranquils early and dump points into Acid Spray to basically clear entire creep waves and the jungle camps if their lane is a little dangerous to stay in.
Just some info that hopefully helps.