The assaults involved a pair attacking other drivers with acid from a moped
A second teenager has been arrested by British police investigating five linked acid attacks in London.
A 15-year-old was arrested on Friday morning on suspicion of grievous bodily harm and robbery following the "hideous" attacks on Thursday night.
A 16-year-old was already being held on suspicion of the same offences after being identified near the scene of the attacks by CCTV.
Britain's Metropolitan Police said they were treating the attacks - which occurred within 90 minutes of each other - as linked.
The assaults involved a pair attacking other moped riders and allegedly trying to steal their bikes.
London police have dismissed rumours all the victims were food delivery drivers set up in advance of the attacks.
Those attacked were described as being "from a variety of backgrounds", while officers urged potential witnesses to come forward with information and photos and videos they may have recorded.
Chief Inspector Ben Clark, from Hackney Borough, said: "These are hideous offences and must have been very frightening for all of the victims."
"Of late we have seen more attacks using corrosive substances in London.
"I would urge businesses and parents to challenge those who they think may be trying to obtain or carry these substances as this could help prevent serious offences and life changing injuries being caused."
At the start of the rampage, a 32-year-old moped rider was approached as he drove along.
The two male suspects tossed the substance in his face before one jumped on his moped and rode away.
Police said the man went to an east London hospital and they are waiting for an update on his injuries.
Twenty minutes later, at 10.50pm, another victim was sprayed with liquid.
The victim was taken to a hospital in the north of the British capital.
At 11.05pm, the two attackers then swooped on a third man, hurling acid in his face.
His injuries are not life-threatening, police said.
Within 15 minutes, they appeared to have struck again, throwing the corrosive liquid at a man causing "life-changing" facial injuries.
The final assault was reported at 11.37pm, when another man was confronted as he sat on his moped in traffic.
He was also sprayed in the face, the moped stolen and both attackers fled.
The victim made his way home before calling police, after which he was taken to hospital with no update on his condition.
A petition to restrict the sale of acid in the UK and bring in a licence system currently has more than 360,000 names.
The head of London's Metropolitan Police, Cressida Dick, said she is looking at whether a change in the law is needed.
She told LBC Radio: "I don't want people to think this is happening all over London all the time, it is really not, but we are concerned because the numbers appear to be going up.
"We will arrest people, we will enforce the law as we can, and we are working very closely with the Home Office to try to see if there is any changes in the law required."
The attacks come days after a man appeared in court charged with throwing acid at a 21-year-old woman and her cousin.
Resham Khan, 21, and Jameel Muhktar, 37, were left with life-changing injuries after the attack in Beckton, east London, on 21 June.
There was another acid attack in east London on Easter Monday, leaving two people at a nightclub partially blinded and others injured.